Professor Michael Stockenhuber

Thermal destruction is a critical cornerstone of addressing the rampant contamination of natural resources with per-and polyfluoroalkyl substances (PFAS). However, grave concerns associated with stack emissions from incineration exist because mechanistic studies have thus far relied on ex situ analyses of end products and theoretical calculations. Here, we used synchrotron-based vacuum ultraviolet photoionization mass spectrometry to study the pyrolysis of a representative PFAS-perfluorohexanoic acid-and provide direct evidence of fluorocarbon radicals and intermediates. A key reaction pathway from perfluorocarboxylic acids to ketenes via acyl fluorides is proposed. We furthermore propose CF2/CF3 radical-centered pyrolysis mechanisms and explain their roles in the formation of other products that may form in full-scale incinerators. These results have not only unveiled the role of radicals and intermediates in thermal PFAS decomposition and recombination mechanisms but also provide unique insight into improving the safety and viability of industrial PFAS incineration.

In this study, we investigated the effect of particle size and solids loading on the magnesite yield in the direct aqueous mineral carbonation of heat-activated lizardite. Experimentation was conducted under single-step reaction conditions (130 bar partial pressure of carbon dioxide (CO2) and 150 °C, with 0.64 M sodium bicarbonate (NaHCO3) and 15 wt% solids) as developed by the Albany Research Center (ARC). The objective of the study was to enhance the understanding of the direct aqueous mineral carbonation process in heat-activated lizardite. Furthermore, we aimed to shed light on how variations in particle size could affect the reaction rate, yield, and the development of protective silica layers. Our experimental data suggest that the extraction of magnesium from finer particles (sub 20 µm) is marginally more effective than from the larger size fractions. This difference likely stems from the larger surface area of fine particles (sub 20 µm) in both low and high solids loading experiments. The highest magnesite yield was 50% after 60 min, and this was achieved for both solids loadings (5 and 15 wt%), demonstrating that the solids loading had no impact on the yield. Our findings indicate rapid heat-activated lizardite reaction within 20 min, which achieved 34% and 40% conversion for 5 wt% and 15 wt% solids loading, respectively. This is followed by declining rates with increasing solids loading.

Atrazine (ATZ) is one of the most widely used herbicides and is highly scrutinized due to its environmental impact. Given its extensive use, ATZ is likely to be exposed to high-temperature conditions such as those encountered during wildfires, incineration, or thermal desorption processes. However, there are limited experimental data on the thermal decomposition of ATZ. The present study investigates the decomposition of ATZ in a flow reactor constructed of a-alumina at temperatures between 400 and 800 °C. At temperatures above 400 °C, thermal decomposition was observed to occur and the formation of HCl and several hazardous chemicals, including hydrogen cyanide and cyanoacetylene were observed during the thermal decomposition of ATZ. Quantum chemical calculations were also performed to elucidate the decomposition pathways and determine the relevant reaction rates. These findings provide crucial insights into the risks associated with exposing ATZ to high temperatures and the potential release of harmful gases from its thermal decomposition.

The excessive availability of coffee-cherry processing residues has garnered attention, owing to potential environmental concerns associated with ground disposal. The current investigation aims to disclose the characteristics of two main coffee agroindustry residues, i.e., coffee pulp and parchment, as well as the resulting biochar which is produced without chemicals and low energy involved. The effects of washing raw biomass on biochar's physical¿chemical properties were investigated. The pre-washed samples were prepared through the following steps: washing, soaking for 20¿h, draining, rinsing, and drying under sunlight for 3¿days. A slow pyrolysis process was performed at 420¿°C in a pilot-scale apparatus to produce biochar. The results show that the pre-washing of feedstock reduced the ash content in coffee pulp biochar from 28.23 to 11.93%. The ash content of coffee parchment biochar decreased from 9.68 to 5.66% as a result of the washing treatment of the raw material. Furthermore, coffee pulp biochar experienced a 25.8% reduction in surface area, while 14% of the coffee parchment was lost due to washing treatment of raw feedstocks. The findings presented in this study offer new insights that are crucial for evaluating the feasibility and advancing the development of a large-scale commercial process for managing coffee agro-industry residues.

Heat treatment of lizardite with a high-flux radiant source to temperatures of up to 630 °C, at rates greater than 10 °C/s and exposure times up to 10 min, is reported for the first time in this study. The novel proposed radiant heat activation process was shown to enhance the subsequent carbonation potential when used as a precursor to dissolution experiments for magnesium extraction. It was found to increase magnesium carbonate yields by up to 58 % following dissolution in a saturated carbonic acid solution at room temperature for 2 h (i.e., exposed to carbon dioxide, CO2, at a partial pressure of 1 atm) compared to the same material heat treated in a rotary kiln. The magnesium extraction from the radiantly heat treated samples was found to: 1) increase monotonically with increasing heat treatment temperature up to 630 °C, 2) increase with increasing holding time at the set heat treatment temperature (up to 480 s), and 3) decrease with increasing heating rates (from 10 to 25 °C/s) for the same heat treatment temperature. Mineral analyses showed that the heat treated samples providing the greatest magnesium extraction had significant dehydroxylation of the crystalline lizardite. The results suggest that the phases formed during heating to moderate temperatures (530 < T < 630 °C) with relatively short exposure times (<10 min) are highly beneficial for magnesium extraction from the particles during dissolution in a carbonic acid solution, potentially improving the subsequent carbonation performance and the viability of using lizardite as the feedstock for long-term, chemically stable storage of carbon.

The thermal decomposition of PFOA was studied in an a-alumina reactor between 400 and 1000 °C under two separate conditions: 1) in a bath gas of air and water vapor (H2O(g)) and 2) in a bath gas of helium, nitrous oxide (N2O) and H2O(g). PFOA decomposition studies undertaken under these conditions, both experimental and modeling analysis, provided insightful information on the conditions leading to the formation of products of incomplete destruction (PIDs). The combination of O2 from air or O from N2O decomposition, combined with H2O(g), resulted in complete mineralization of PFOA at temperatures above 950 °C into HF and CO2. An elementary mass balance of F and C atoms concluded that, at 1000 °C, 105 ± 10 % of F atoms present in PFOA are converted into HF, while 100 ± 5 % of C atoms into CO2. Both H2O(g) and oxygen together are necessary for complete mineralization.

The major aim of this research was to understand the effect of the addition of sodium bicarbonate (NaHCO3) on the reaction yield and products in the direct aqueous mineral carbonation of heat-activated lizardite under single-step reaction conditions (130 bar, 150 °C) developed by the Albany Research Center. This was achieved by tracking the evolution of the aqueous and solid species produced over the duration of the reaction. Analysis of solid and liquid samples was performed using a variety of analytical techniques, including thermal gravimetric analysis mass spectrometry, inductively coupled plasma optical emission spectrometry, qualitative and semiquantitative X-ray diffraction analysis, and laser diffraction particle size analysis. Carbonation experiments were conducted with and without NaHCO3 using heat-activated lizardite to study its effect on the reaction rate and overall yield. It was found that NaHCO3 controlled the magnesium carbonate phase formed in the carbonation reaction [hydromagnesite or magnesite (MgCO3)]. It can be concluded that NaHCO3 elevates the concentration of carbonate ions (CO32-), leading to a heightened level of supersaturation in the carbonate phase. This, in turn, contributes to an increased extent of MgCO3 precipitation.

Various reactor tubes (quartz, stainless steel 316 and stainless steel 253 MA) were used to examine their influence on the thermal decomposition of perfluorooctanesulfonic acid (PFOS) between 400 and 1000 °C. Using helium as a carrier gas, with the addition of 100 ¿ 300 ppm of PFOS to the feed gas, the influence of the reactor materials on PFOS decomposition was studied. The quartz reactor led to a notable reduction in the concentration of HF and substantial quantities of SiF4 were observed. Stainless steel 316 produced C2F4, HF, COF2 and SO2 as its primary products up to 800 °C. However, at temperatures above 800 °C, near quantitative removal of SO2 from the gas phase was observed, with the concomitant formation of a blue molybdenum sulfur complex. Stainless steel 253 MA, the composition of which contains over 1% Si produced substantial quantities of SiF4 but no significant decrease in the gas phase concentration of HF. Environmental implication: This research underscores the significant role of reactor material in the thermal treatment of PFAS, a globally widespread and enduring environmental contaminant. The findings have direct implications for the optimization of thermal treatment strategies aimed at mitigating PFAS contamination. The insight into how different reactor materials interact with PFOS during thermal treatment expands our understanding of potential destruction methods. This knowledge is crucial in the development of effective, sustainable strategies for managing persistent environmental pollutants like PFAS.

Green diesel produced from palm fatty acid distillate (PFAD) could decrease reliance on fossil fuels and GHG emissions. Thus, this work reports a solventless hydrodeoxygenation (HDO) reaction using zeolite beta and La-zeolite beta (LZ) to convert PFAD into diesel-rich fuel. Specifically, LZ-catalyzed reaction dominated the hydrocarbon fraction over zeolite beta with high HDO and DO activity. Lewis' acid sites remove oxygenated species, while Brønsted acid sites aid in cracking. Since most HDO reactions happened on LZs' exteriors, pore size did not affect HDO. The HDO optimum reaction activity was attained at 400 °C using 1 wt% of LZ under 5 MPa H2 pressure within 3 h. LZ showed 84 % diesel selectivity and greater hydrocarbon output in the N2 flow environment (DO reaction) than the H2-reaction conditions. The H2 atmospheric reaction system prevented LZ coking, confirming its effect on catalyst stabilisation. The HDO process yielded a paraffinic hydrocarbon product with ~73 % selectivity of hexadecane (C16H34), demonstrating the formation of liquid fuel with reduced oxygenates. A vacuum distillation technique purified the crude liquid product (CLP) into a refined liquid product (RLP) with 99 % diesel component renewable diesel (RD 100) met ultra-low sulfur diesel requirements that closely resemble those derived from petroleum. This affirms that the high-quality R100 can be used in existing diesel engines efficiently without modifications. Based on reusability studies, the LZ catalysts are capable of performing HDO and DO for up to 5¿6 cycles, proving their positive impact on process efficiency and catalyst longevity. Overall, the LZ-catalyzed hydrogen-assisted process is a more promising technology for the oil and gas industry, where hydrogen can be produced from various refinery feedstocks, hence, its implementation could significantly enhance efficiency and sustainability in refining operations.

Natural clinoptilolite (coded as Escott), synthetic BEA, and mixed Escott-BEA zeolites supported nickel and iron catalysts were employed for catalytic hydropyrolysis of eucalyptus globulus leaves. Comparing non-catalytic pyrolysis and catalytic pyrolysis in N2, the use of catalysts along with H2 (30 bar) resulted in improved yields of liquid oil and gas products, with reduced production of biochar/coke. Moreover, the biochar from catalytic hydropyrolysis showed a higher mesopore surface area (97 m2/g) than non-catalytic biochar (74 m2/g). Incorporating a small amount of BEA into Escott weakens the metal-support interaction, enhances H2 adsorption activity and increases the catalyst acidity, leading to an improved aromatic monomers selectivity while preventing excessive cracking of liquid oil. Consequently, Ni-Fe/Escott-BEA catalyst shows the highest content of valuable liquid organic components. Ni-Fe/Escott, with the largest Ni particles and lowest acidity, exhibits higher selectivity to methane and naphthalenes products. In contrast, Ni-Fe/BEA with excessive acid sites exhibited significantly lower content of liquid organic products but higher yields of C2-C5 gas products and deposited carbon, primarily ascribed to its high acidity promoting coupling, cracking and deoxygenation reactions. The deactivation of Brønsted acid sites was more pronounced than Lewis acid sites, underscoring their crucial role in coupling reactions and leading to increased coke deposition.

Utilizing air (O2) as the bath gas at reaction temperatures between 500 and 1000 °C, the thermal decomposition of perfluorooctanesulfonic acid (PFOS) in an a-alumina reactor was studied. It was found that in an air bath gas (and in the absence of water vapor), COF2 and trace amounts of C2F4 were detected. Quantum chemical calculations at the G4MP2 level of theory confirmed that CF2 radicals can react with O2 to form COF2 and an O (3P) atom. The inclusion of 2000 or 20 000 ppmv of water vapor (H2O(g)) to the air bath gas proved to be the key step to mineralizing all PFOS into hydrogen fluoride (HF), CO2, and SO2. At temperatures above 850 °C (0.95-0.84 s residence time), a feed of 20 000 ppmv of H2O(g) in air was observed to produce a product stream in which no gaseous fluorocarbon products were detected, with only HF, SO2, and CO2 being produced. A sulfur balance confirmed that 100 ± 5% of all the S in PFOS had converted into SO2 with a chemical kinetic model predicting in excess of 99.99999% destruction removal efficiency of PFOS at temperatures above 700 °C. Furthermore, from an elementary balance of F and C atoms, it was determined that at 1000 °C, approximately 99 ± 5% of F atoms present in PFOS have been converted into HF, and approximately 100 ± 5% of C atoms had been converted into CO2. A chemical kinetic model was developed to understand the importance of both O2 and water vapor in the overall thermal decomposition of PFOS, leading to complete mineralization. In the presence of both O2 and H2O(g), it was found that relatively high concentrations of OH radicals were produced, with significant contribution to OH formation attributed to the well-known chain branching reaction O(3P) + H2O ¿ OH + OH.

The effect of desilication on the physic-chemical properties of ferrierite zeolite was investigated using spectroscopic and solid characterisation techniques including N2-adsorption, XRD, SEM, H2-TPR, NH3-TPD and in situ FTIR. Stability of active oxygen species formed from N2O over the Fe-FER catalysts and the catalytic activity for direct conversion of methane to value-added products at temperatures between 300 °C and 400 °C were studied. Ferrierite zeolites, pre-treated with 0.1 M, 0.2 M and 0.3 M NaOH solutions preserved the crystal structure of the ferrierite zeolite but their textural properties were significantly modified, leading to an increase in mesopore area and creating a greater concentration of terminal Si-OH groups, concomitant with increase in the amount of extra-framework Al and reduction in the number of bridging Si-OH-Al species. Batch-mode catalytic reaction studies of methane with N2O conducted in an in situ FTIR cell demonstrate that the methoxy groups formed on extraframework iron sites followed by the migration of these species to silicon defect sites, which resulted in a decline in the intensity of terminal Si-OH groups bands in the IR spectra. N2O-TPD experiments confirm that N2O is converted to N2, O2 and NO over Fe-FER catalysts at 350 °C. The decline in the desorption temperature of these products observed over Fe-FER catalysts treated with alkaline solution is consistent with a significant increase in the mesopore surface area from 28.3 m2/g to 102.4 m2/g. The peak areas of desorbed O2 and NO were estimated, and the different ratios of O2/NO observed on these catalysts appears to be related to the difference stabilities of surface oxygen species. Studies under continuous reaction conditions demonstrate that, at a similar level of methane conversion (ca. 2.8 %), Fe-FER catalysts prepared with the moderately alkaline solution (0.2 M NaOH) results the highest yield of methanol, dimethyl ether and formaldehyde. It is asserted that this enhanced selectivity is the result of the comparatively high concentrations of terminal silanol groups, Brønsted-acid sites, stability of active oxygen species and mesopore volume.

In the present study, a series of La-HZSM5 catalysts were prepared through wet impregnation and investigated for the production of premium quality diesel fuel via hydrodeoxygenation (HDO) of oleic acid (OA). Several parameters were evaluated, such as reaction temperature (360¿400 °C), H2 pressure (1¿5 MPa), La concentration (5¿20%), catalyst loading (1¿7 wt%), and reaction time (1¿4 h). At a reaction of 400 °C for 2 h under 5 MPa H2 pressure, the La(10)HZSM5(90) catalyst showed 97% hydrocarbon yield with 92% of diesel selectivity. The superior HDO activity by La(10)HZSM5(90) in producing high quality diesel is due to a sufficient number of weak + medium acid sites and its mesoporous structure. Vacuum distillation was complementary for producing high quality diesel fractions consisting of C17 fractions. The reusability of the La(10)HZSM5(90) catalyst was also demonstrated, though the catalyst still had coking activity.

Ion exchanged Ru/ZSM-5 and Ru/BEA catalysts, prepared by replacing the extra framework NH4+ cations in zeolites with Ru3+ ions, are employed for the hydrodeoxygenation of guaiacol. The performance results indicate ion-exchanged Ru zeolites, with extremely low Ru contents (~0.2 wt%), possess a high intrinsic HDO activity compared to the catalysts prepared by the incipient wetness impregnation method. On the basis of TEM, FTIR, XPS and TPD analysis, the NH4+ ions in zeolite were substituted by Ru species, with metal particles entered the zeolite cages and finely dispersed on the support. These ion-exchanged Ru particles exhibit a strong electronic interaction with oxygen atoms of zeolite framework with a mixed Ru(0)-Ru(III) species observed in the reduced samples. In contrast, only Ru0 was detected in the reduced impregnated Ru/ZSM-5. The partial-reduced Ru species over the ion-exchanged Ru/ZSM-5 catalyst shows a high H2 adsorption activity facilitating the hydrogenation of guaiacol to the saturated products (such as 2-methoxycyclohexanol). In addition, ion-exchanged Ru-ZSM-5 and Ru-BEA catalysts present a similar normalized cyclohexane formation rate (based on the concentration of acid sites), suggesting the acid sites play a pivotal role in the deoxygenation of 2-methoxycyclohexanol to cyclohexane.

In this study, various metal-modified zeolite beta-based catalysts such as La(10)zeo(90), Co(10)zeo(90), Fe(10)zeo(90), Mg(10)zeo(90), Mn(10)zeo(90) and Zn(10)zeo(90) were investigated in the hydrodeoxygenation (HDO) of oleic acid (OA) to produce renewable diesel. The La(10)zeo(90) catalyst showed a conversion of OA up to 99 % with 83 % C15 and C17 selectivity after the reaction at 350 °C for 2 h under 4 MPa H2 pressure. The superior activity of La(10)zeo(90) was attributed to the synergistic interaction between La-Si-Al, a sufficient amount of weak + medium acid sites and excellent textural properties (large pore diameter). Larger pore diameter of La(10)zeo(90) is highly desirable as it will generate greater diffusion of bulky molecules, thereby improving the accessibility of the reactant and hence excellent catalytic activity. The vacuum distillation was used to purify the crude liquid product (CLP), producing high-quality diesel fractions mainly comprising C14, C15, and C17 fractions.

This work investigates chemical stability of Mg-silicates and silica in aqueous systems in order to gain in-depth understanding of their dissolution and precipitation behaviour under different conditions. The aim was to utilise the knowledge gained to develop an engineered carbon mineralisation technology for an efficient and cost competitive CO2 capture and utilisation. The results, based firmly on 29Si solid-state MAS NMR spectroscopy, and complementary techniques, demonstrate the influence of Si coordination (Qn) on the extent of Mg-silicates dissolution, as the increase in the number of neighbouring Si atoms in the structure of Mg-silicates reduced dissolution of Mg-silicates. While 100 and 80% of Q1(3 Mg) Mg-silicate dissolved in pH = 5 and 6.5, the extent of dissolution for Q2(2 Mg) was lower at values of 90 and 65% under the same conditions, while Q3(1 Mg) did not actually dissolve in solutions with pH = 5 and 6.5. The results of precipitation studies indicated the effect of Mg solubility on the structure and Mg content of the precipitated phases. While Mg-silicates with all three structures of Q1(3 Mg), Q2(2 Mg) and Q3(1 Mg) precipitated in the mildly alkaline environment (pH = 8.5) with the ratios of 20, 40 and 40% respectively, in concentrated acidic solutions of pH = 0, only pure silica (no Mg content) with Q3(1H)/Q4(0H, 0 Mg) having a ratio of 35 and 65% precipitated. The results of direct and indirect carbon mineralisation experiments showed that only 40 and 57 wt% of Mg content of thermally treated Mg-silicate was extracted respectively, consistent with 29Si NMR analyses, indicating that only intermediate Mg-silicate phases I and II with Q1(3 Mg) and Q2(2 Mg) structures were reactive, while other Mg-silicate phases remained inert. Another reason for limited Mg extraction in direct and indirect carbon mineralisation experiments is related to precipitation of a silica-rich phase/s on the surface of the reacting particles leading to passivation, again consistent with 29Si NMR analyses. This confirmed precipitation of Mg-silicate with a Q3(1 Mg) structure as well as hydrated silica Q3(1H) and silica Q4(0H, 0 Mg) in aqueous environments, similar to carbonation processes.

Formation of silica-rich passivation layers formed on the periphery of reacting feed particles is one of the primary obstacles in obtaining high magnesite yields during direct aqueous mineral carbonation of peridotites and serpentinites. The disruption of the silica-rich layer around partially reacted grains as a result of concurrent grinding on the degree of carbonation (magnesite yield) was investigated in this work. Three types of naturally-occurring magnesium silicate feedstocks, dunite, olivine and lizardite, as well as three types of grinding media, were examined. Discrete size fractions of feed samples, with and without grinding media, were carbonated. SEM readily disclosed the formation of a silica-rich shell around a magnesium rich core during carbonation. EDS analysis was employed to study the elemental composition of reacted particles' shell and core. The method confirmed that during concurrent grinding these silica-rich layers were removed and continuously produced a fresh surface available for further reaction. The removal of the silica-rich layer was shown to significantly improve magnesite yields up to a 600 % increase in yield. Among the three different grinding media used in this work, zirconia and stainless steel media resulted in similar and highest magnesite yields, which is believed to be due to a combination of their high densities and hardness. The findings of this research showed that enhanced magnesite yields could be achieved for all feedstock without the need for energy intensive pre-treatment steps (e.g. ultrafine grinding and heat-activation). Moreover, concurrent grinding resulted in a magnesite yield when raw lizardite was carbonated.

Hydrodeoxygenation (HDO) of guaiacol was investigated over BEA-supported bimetallic Ni-Fe, Ni-Mo, and Ni-W catalysts in a continuous-flow reactor. The electronic properties of Ni were significantly modified following the addition of W and Fe as analyzed by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), which is well in line with density functional theory (DFT) calculations, suggesting that the formation of Ni-Fe and Ni-W alloys is thermodynamically favorable while the generation of a Ni-Mo alloy is unfavored. The HDO over 9 wt % Ni/BEA catalyst was significantly improved following the incorporation of small quantities (<2.2 wt %) of Mo or Fe, while the incorporation of W decreased the HDO rate. The selectivity to hydrogenation products over the Ni-Fe/BEA catalyst was not altered compared to that of Ni/BEA during the hydrogenation of toluene, indicating that the observed increase in guaiacol conversion was engendered by the promotion of the direct hydrogenolysis of guaiacol to aromatics over Ni-Fe species. The hydrogenation and HDO rates of the Ni-Mo/BEA catalyst were both higher than those of Ni/BEA, which was attributed to the increased Ni dispersion promoted by Mo as indicated by similar nickel turnover frequency (TOFNi) values observed over Ni/BEA and Ni-Mo/BEA.

Catalysts with different iron species distributions were developed by loading iron ions to ferrierite (FER) zeolite using liquid ion exchange (IE) and solid state ion exchange (SSIE) methods, which in turn facilitates to study the relation between the nature of iron sites with the formation and stability of surface oxygen species, based on the comparable investigation of catalytic activity and selectivity to products over the catalysts, and the characterisation results obtained from a variety of spectroscopic and solid characterization techniques. IR spectra and NH3-TPD profiles demonstrate a greater extent of exchange of protons in bridging OH positions by iron cations with the Fe-FER-SSIE, in comparison to Fe-FER-IE catalyst. The primary catalytic species present in Fe-FER-IE are isolated Fe species in cation exchange positions, as indicated by UV¿vis spectra, while isolated and oligomeric extra-framework Fe species were present in Fe-FER-SSIE catalysts, which is consistent with H2-TPR profiles of N2O pre-treated catalysts and IR spectra of NO adsorption on the catalysts. N2O-TPD results demonstrate that the desorption of oxygen molecules (O2) released from surface oxygen species was observed at lower temperature and higher concentration from Fe-FER-IE than Fe-FER-SSIE. Higher ratio of N2O consumption/methane conversion over Fe-FER-IE was observed than Fe-FER-SSIE. With similar methane conversion, over Fe-FER-SSIE a higher selectivity to valuable products methanol, formaldehyde and dimethyl ether was observed than over Fe-FER-IE.

Kinetics of pyrolysis of the pollutant perfluorooctanesulfonic acid (PFOS) in inert bath gases have been studied in two flow reactors constructed of a-alumina and of stainless steel (SS) at temperatures between 400 and 615 °C. Results from the SS reactor give support to previous and our own quantum chemical calculations based on smaller perfluorinated sulfonates, according to which initiation of decomposition of PFOS first takes place by elimination of HF to form an unstable a-sultone with a rate constant, k1. The sultone then rapidly liberates SO2 and forms perfluorooctanoyl fluoride with a rate constant, k2 with k2 » k1 such that the overall rate constant k' ¿ k1. Products observed from both reactors in the above temperature range comprised HF, SO2, and perfluorooctanoyl fluoride. The value of the rate constant for the formation of HF and SO2 measured in the SS reactor was found to be k1 = (1.3 ± 0.5) × 1014 exp(-253 ± 5 kJ/mol/RT) s-1.

Natural and synthetic (BEA, MOR) zeolite-supported nickel (~5 wt%) catalysts were prepared and employed for the hydrogenation of toluene and hydrodeoxygenation of anisole in a continuous-flow reactor. Ni/BEA and Ni/MOR display a higher level of metal dispersion and stronger metal-support interaction compared to the Ni/NZ and Ni/Escott catalysts, resulting in a higher concentration of charge-compensating Ni species and a larger high-temperature reduction peak. The Ni/BEA and Ni/MOR also present a significant mass of low-temperature desorbed H2(centred at 150 °C) based on H2-TPD, suggesting the H species are weakly adsorbed on small Ni clusters. In contrast, the H species were strongly adsorbed by the bulk Ni crystal over Ni/Escott and Ni/NZ, which were desorbed at maxima between 211 and 222 °C. We propose that the strongly adsorbed H species play a crucial role in the hydrogenation of toluene, leading to a significantly higher yield of methylcyclohexane over Ni/Escott and Ni/NZ compared to Ni/BEA and Ni/MOR. Both metal and acid sites are required in the hydrodeoxygenation of anisole. The strong Brønsted acid sites and numerous smaller Ni species over Ni/BEA facilitated the transalkylation of anisole to phenol and methylanisole and subsequently hydrogenolysis of phenol to benzene, followed by the hydrogenation of benzene to cyclohexane.

This study investigated the hydrodeoxygenation (HDO) of oleic acid (OA) that is abundantly found in palm oil for the production of renewable diesel. The effectiveness of mesoporous catalysts, HZSM-5 and zeolite beta, in favoring diesel hydrocarbons was determined. The catalysts were activated by calcination at 550¿°C for 5¿h and their physicochemical properties were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed desorption using ammonia probe molecules (TPD-NH3), and Brunauer¿Emmett¿Teller analysis (BET). XRD analysis of both zeolite beta and HZSM5 showed high crystalline size of 24 and 84¿nm, respectively. BET analysis found that the zeolite beta catalyst had a greater surface area (648 m2¿g-1) than HZSM5 (465¿m¿g-1) without significant differences in pore size and volume. According to the TPD-NH3 study, zeolite beta had the most weak + medium acid sites when compared to HZSM5. It should be noted that HZSM5 also demonstrated the presence of strong acid sites. The optimal conditions for both catalysts were 350¿°C, 4¿MPa hydrogen pressure, and 5% catalyst load over a 2¿h reaction period. From the results, the zeolite beta exhibited superior HDO reaction activity than HZSM5 with diesel selectivity ~ 77%.

The in situ X-ray absorption fine structure (XAFS) was measured in the titanium-peroxo system supported by titanium silicalite-1 (TS-1). After this, the complex was heated, in line with previous in situ FTIR studies, in order to reproduce the catalytic conditions in those studies which demonstrate a reaction pathway to reaction products other than epoxides, namely, carbonyls, which have not been reported previously on this type of catalyst.

BEA supported Ni-Fe catalysts, prepared by various impregnation techniques, were characterised and examined for their activity for the hydrodeoxygenation (HDO) of guaiacol and hydrogenation of toluene. The aim of the study was to explore the factors affecting the formation of Ni-Fe active species and explore the relationship between the concentration of surface Ni, Ni-Fe species and HDO activity. Catalysts prepared initially with Fe, or co-currently with Fe and Ni exhibited a higher level of HDO rate compared to catalyst that was prepared with Ni initially. When a catalyst was impregnated initially with Fe, metal-supported interaction was relatively weak, thus the formation of Ni-Fe species was promoted. In contrast, a reduced number of Ni sites was involved in the formation of Ni-Fe species when the catalyst was initially impregnated with Ni, resulting in a low HDO rate. The rate of cyclohexane formation is proportional to the concentration of surface Ni-Fe over the catalysts with similar Ni and Fe loadings but prepared by different impregnation sequences. The enhanced HDO rate is attributed to the hydrogenolysis activity of Ni-Fe species. The effect of Ni/Fe ratio on HDO activity was also investigated under differential conditions and the catalyst with a Ni/Fe mass ratio of 3.3 exhibited the highest rate of cyclohexane formation.

To overcome diffusional limitations associated with the catalytic cracking of large hydrocarbons, a novel core-shell hierarchical zeolite has been developed and evaluated. Large, branched hydrocarbons encounter diffusional limitations in micropores of zeolites for cracking reactions, a limitation overcome by improved textural properties of hierarchical zeolites, leading to enhanced cracking activity. This will result in an improvement in deactivation rate, cracking activity, and enhanced product selectivity towards light hydrocarbon products. The impact of chain length involving a long chain paraffin (hexadecane) and a highly branched aromatic (1,3,5-TIPB) was also investigated to study the influence of the presence of the micro-mesopore network in overcoming diffusion limitations. This paper investigates the use of hierarchical core-shell BEA@NanoZSM-5 in the catalytic cracking of 1,3,5 triisopropylbenzene (1,3,5-TIPB), and n-hexadecane (C16). The novel hierarchical composite was synthesized by preliminary seeding of the core BEA crystals and subsequent growth under hydrothermal conditions leading to the formation of an intergrown and distinctive nanocrystalline ZSM-5 shell zeolite. Evidence of the existence of a hierarchical structure was probed by Ar sorption utilising non-local density functional theory (NLDFT) pore size distribution analysis.

Chlorpyrifos (CPF) is a widely used pesticide; however, limited experimental work has been completed on its thermal decomposition. CPF is known to decompose into 3,5,6-trichloro-2-pyridinol (TCpyol) together with ethylene and HOPOS. Under oxidative conditions TCpyol can decompose into the dioxin-like 2,3,7,8-tetrachloro-[1,4]-dioxinodipyridine (TCDDPy). With CPF on the cusp of being banned in several jurisdictions worldwide, the question might arise as to how to safely eliminate large stockpiles of this pesticide. Thermal methods such as incineration or thermal desorption of pesticide-contaminated soils are often employed. To assess the safety of thermal methods, information about the toxicants arising from thermal treatment is essential. The present flow reactor study reports the products detected under inert and oxidative conditions from the decomposition of CPF representative of thermal treatments and of wildfires in CPF-contaminated vegetation. Ethylene and TCpyol are the initial products formed at temperatures between 550 and 650 °C, although the detection of HOPOS as a reaction product has proven to be elusive. During pyrolysis of CPF in an inert gas, the dominant sulfur-containing product detected from CPF is carbon disulfide. Quantum chemical analysis reveals that ethylene and HOPOS undergo a facile reaction to form thiirane (c-C2H4S) which subsequently undergoes ring opening reactions to form precursors of CS2. At elevated temperatures (>650 °C), TCpyol undergoes both decarbonylation and dehydroxylation reactions together with decomposition of its primary product, TCpyol. A substantial number of toxicants is observed, including HCN and several nitriles, including cyanogen. No CS2 is observed under oxidative conditions-sulfur dioxide is the fate of S in oxidation of CPF, and quantum chemical studies show that SO2 formation is initiated by the reaction between HOPOS and O2. The range of toxicants produced in thermal decomposition of CPF is summarised.

The rate-determining step in the aqueous carbonation of serpentine minerals is the dissolution of Mg from serpentine. The dissolution rate of minerals largely depends on the pH of the solution and the size of serpentine particles. In the present work, an experimental method has been developed to study the dissolution rate of heat activated serpentine (lizardite polymorph) in a wide range of pH, solid to liquid ratio and particle size at room temperature. The results allowed us to determine the effect of these variables on the dissolution kinetics of heat activated lizardite, which represents crucial kinetic data for accurately modelling the carbonation rates of serpentinite. Additionally, amorphous Si re-precipitation at high solid to liquid (S/L) ratio and pH 6.1 was demonstrated. These provide essential data for the design and optimisation of industrial mineral carbonation processes. For the first time, the crackling core model (CCM) was applied to model the dissolution kinetics of heat activated lizardite in acidic solutions. Applying the CCM model to a wide range of particle sizes provides useful information on the mechanism of the dissolution of heat activated lizardite and the range of particle size for which the assumptions of the model are valid. Characterising serpentine particles leached under different conditions, along with analysing model parameters, provided a new insight into the mechanism of the dissolution of heat activated lizardite.

This paper presents the results of dichloromethane (DCM) decomposition to polymers utilising dielectric barrier discharge under non-oxidative reaction conditions. The conversion levels, mass balance, reaction mechanism and polymer characterisation in relation to DCM reaction are presented in this paper. Reaction pathways describing the decomposition of DCM and subsequent formation of the major products are outlined. Speculation of the mechanism of formation of CHCl3 and C2HCl3 are supported by quantum chemical calculations. In addition, the effect of introducing methane in the reaction feed on the conversion level of DCM and the polymer structure is also examined in this paper.

This work has used high range imaging mass spectrometry to study a coal sample that has undergone heating with a temperature gradient. A custom made hotplate was heated to 1000°C and the coal was allowed to heat naturally through conduction to produce a large thermal gradient typical of conditions in a coke oven. The sample was quenched, sectioned and analysed using laser desorption time of flight imaging mass spectrometry (LDI-TOF-IMS) to study the molecular changes that occur within the plastic layer and in the semi-coke. The raw coal was observed to have a molecular weight range between 500 and 20,000 Da with a peak occurring at 2000 Da. The plastic layer was observed to have a prevalence for increasing 500-1000 Da structures though this formed part of the larger molecular weight range. Resolidification of the plastic layer coincided with a rise in 4000 Da structures. The semi-coke spectrum had a series of repeating peaks separated by 24 Da extending from 1000 Da to 3000 Da. This was considered evidence of broad molecular ordering. A second phenomenon was observed in the semi-coke associated with low range molecular weights (50-300 Da). This appeared as high intensity signals in a molecular range typically considered as ion fragments (being too low in size to remain in the high vacuum environment). It was speculated that these low range structures may be associated with the coking of volatile tars exiting the hot-side of the plastic layer through high temperature semi-coke. Overall, this preliminary work provides a novel methodology to study the heating impacts during coking on a molecular level.

A novel Pd supported on TS-1 combustion catalyst was synthesized and tested in methane combustion under very lean and under highly humid conditions (<1%). A notable increase in hydrothermal stability was observed over 1900 h time-on-stream experiments, where an almost constant, steady state activity obtaining 90% methane conversion was achieved below 500 °C. Surface oxygen mobility and coverage plays a major role in the activity and stability of the lean methane combustion in the presence of large excess of water vapour. We identified water adsorption and in turn the hydrophobicity of the catalyst support as the major factor influencing the long term stability of combustion catalysts. While Pd/Al2O3 catalyst shows a higher turn-over frequency than that of Pd/TS-1 catalyst, the situation reversed after ca. 1900 h on stream. Two linear regions, with different activation energies in the Arrhenius plot for the equilibrium Pd/TS-1 catalyst, were observed. The conclusions were supported by catalyst characterization using H2-chemisorption, TPD, XPS analyses as well as N2-adsorption-desorption, XRD, SEM, TEM. The hydrophobicity and competitive adsorption of water with oxygen is suggested to influence oxygen surface coverage and in turn the apparent activation energy for the oxidation reaction.

In this contribution, the development of a process for the synthesis of potentially highly valuable polymeric products from the reaction of waste glycerol with ammonia is reported for the first time. The polymers were the result of a single step, continuous gas phase process, catalysed by an alumina-supported iron catalyst, operating under relatively mild reaction conditions. The solid product was characterised using 1D and 2D NMR spectroscopy, FTIR spectroscopy, qualitative chemical tests and elemental analysis. Characterisation revealed building blocks with unsaturated, amido and ester functionalities shaping a mixture of polymers. Nitrogen atoms were present in the main chain of the resultant polymers. NMR analyses of the polymer denotes the formation of structural defects such as unsaturation and branching; whilst the partial solubility of the polymer in solvents such as CDCl3 and THF is indicative of the formation of cross-linked structures. Insights into the mechanism of formation of these functional groups were based on the liquid and gas phase product distribution. Polymers with chain structures similar to those synthesised in this work are currently manufactured from fossil fuels and are widely used in biomedical applications not only because of their architecture but also due to their response to changes in pH and temperature.

An increased interest in using hydrocarbons in solid oxide fuel cells for the production of power has led to research into operation on synthesis (syn) gas, a mixture of hydrogen and carbon monoxide. Hydrocarbons are typically reformed, either internally or in an external reformer prior to the fuel cell, producing syngas with various H2:CO ratios depending on the hydrocarbon used. This paper examines the effect of varying the H2:CO ratio with respect to C1 to C4 steam reforming reactions and additionally a mixture containing a higher ratio of carbon monoxide. It was found that there was no significant relationship between cell performance and H2:CO ratio when a high feed rate was employed. For low flow rates, however, the high carbon monoxide concentration resulted in a significant decrease in cell performance. It was determined that this was caused by reversible carbon deposition as opposed to a decrease in carbon monoxide reactivity.

Nano-sized Co3O4, Fe2O3, Au/Co3O4 and Au/Fe2O3 catalysts were prepared and evaluated for catalytic combustion of lean methane-air mixtures. Characteristics and catalytic activities under dry and wet feed conditions were investigated at gas hourly space velocities up to 100 000 h-1 mimicking the typical flow and conversion requirements of a catalytic system designed to treat a ventilation air methane stream. In order to gain a better understanding of the interaction between H2O and the catalyst surface, temperature-programmed desorption of water over fresh and used samples were studied, and supported by other catalyst characterization techniques such as N2-adsorption desorption, XRD, TEM, SEM and XPS analyses. The activity measurements of the catalysts studied identify Co3O4 as the most active material. Co-precipitating gold particles with cobalt oxide or iron oxide do not enhance the activity of the catalyst, which is most likely due to blocking the active site of support by the gold particle. The presence of strong hydroxyl bonds on the catalyst surface is substantiated by TPD and XPS analyses, and is suggested to be responsible for the rapid deactivation of Fe2O3 and Au/Fe2O3 catalysts.

© 2014 Elsevier B.V. All rights reserved. Reagents from a base catalysed condensation reaction (Knoevenagel condensation reaction between ethyl cyanoacetate and benzaldehyde), were adsorbed on ZnO and Al < inf > 2 < /inf > O < inf > 3 < /inf > catalyst surfaces and subject to temperature programmed desorption experiments, monitored using mass spectrometry. Ethyl formate, ketenimine species, carbon dioxide and carbon monoxide were desorption products from ethyl cyanoacetate, while benzene, carbon dioxide and carbon monoxide were desorbed from the catalysts loaded with benzaldehyde. The formation of the ketenimine species was confirmed by in situ FTIR experiments. The observation of the decomposition species further substantiates a proposed reaction mechanism for the Knoevenagel condensation reaction on the catalyst surface of some oxide catalysts.

Reaction of phenol with hydrogen peroxide over H-MFI, Fe-MFI, H-BEA, Fe-BEA and TS-1 zeolite catalysts was investigated. Over H-BEA, biphenyl product was observed. It is suggested, that the larger pore size of H-BEA facilitates coupling of two phenol molecules. Two distinct reaction mechanisms are proposed for acid and redox catalysts. © 2013 Springer Science+Business Media New York.

In this paper we focus on the development of a methodology for treatment of carbon tetrachloride utilising a non-equilibrium plasma operating at atmospheric pressure, which is not singularly aimed at destroying carbon tetrachloride but rather at converting it to a non-hazardous, potentially valuable commodity. This method encompasses the reaction of carbon tetrachloride and methane, with argon as a carrier gas, in a quartz dielectric barrier discharge reactor. The reaction is performed under non-oxidative conditions. Possible pathways for formation of major products based on experimental results and supported by quantum chemical calculations are outlined in the paper. We elucidate important parameters such as carbon tetrachloride conversion, product distribution, mass balance and characterise the chlorinated polymer formed in the process. © 2014 Elsevier B.V.

Conversion of glycerol to allyl alcohol was carried out over an iron on alumina catalyst. With the aim of enhancing selectivity towards the desired product and to reduce acrolein formation (a detrimental impurity in the subsequent epoxidation of allyl alcohol) the supported iron catalyst was modified using alkali metals. It was found that lithium, sodium, potassium, rubidium and caesium deposition on the catalyst surface increased allyl alcohol yield and reduced the rate of catalyst deactivation. Coincidently, acrolein selectivity decreased by up to 75% following treatment with the alkali salt.Changes in the product distribution were determined to be associated with altering the acid/base properties of the catalyst, as confirmed by isopropanol dehydration/dehydrogenation, ammonia and carbon dioxide temperature programmed desorption. The treatment was also found to influence the physical properties of the catalyst surface. A correlation between acid to basic site concentration and allyl alcohol selectivity was established. A reduction in the former value results in an enhancement in the rate of allyl alcohol formation. A reaction mechanism was developed based on the effect of iron and alkali metals catalysing the conversion of glycerol into allyl alcohol. The proposed catalyst modification technique is a straightforward method, readily applicable at a larger scale due to the simplicity of the alkali inclusion and its striking influence on the reaction selectivity. © 2014.

In this paper, we report new insights into the deactivation phenomenon of palladium based catalysts for catalytic combustion of ventilation air methane (VAM). It was found that the primary factor responsible for low temperature catalyst deactivation is the water vapour present in the feed stream. The influence of water vapour on VAM was examined by comparing the properties of fresh catalysts with catalysts following over 1000 h reaction time-on-stream. The techniques applied to characterize the catalysts included TPD, XRD, N 2-isotherm adsorption, H2-chemisorption and XPS analyses. Alternating between dry and water vapour-saturated VAM feed disclosed ca. 50% reversible drop in activity. XPS analysis suggests an absence of a palladium hydroxide phase during the initial 2 h on stream, although prolonged exposure to the reactant leads to the formation of palladium hydroxide, which appears to match the progressive deactivation of the Pd/Al2O3 catalyst. Introduction of VAM dust (a mixture of fine coal, CaCO3 and aluminosilicate particles) causes a variation in catalytic activity originating from coal-dust ignition and the effect of chloride on the surface of the catalyst. In the presence of these inhibiting agents, an average methane conversion of higher than 75% over 1100 h was achieved at reaction temperatures below 600°C. This journal is © the Partner Organisations 2014.

A continuous process for the conversion of glycerol to allyl alcohol, where ammonia or organic acids are added to the feed as sacrificial reductants, was investigated. Significant enhancement on the rate of formation and yield of the allyl alcohol is observed with some of the reducing agents examined over an alumina-supported iron catalyst. Optimising the molar ratio of the reductant relative to feed glycerol results in an increase in the yield of allyl alcohol from 9% (in the absence of additives) to 11.3% with ammonia, 15.1% with ammonium hydroxide, 17.8% with oxalic acid and 19.5% with formic acid. Moreover, the addition of other organic acids, which are produced in a typical glycerol conversion experiment, was studied. However, acetic and propanoic acids had little effect on the rate of formation of allyl alcohol. Analysis of the product distribution in the liquid and gas phases when oxalic and formic acids were added suggests a two-step process for the formation of allyl alcohol under the operating conditions of the reaction; the initial step involves the dehydration of glycerol while the second comprises the reduction of the species produced in step one. © the Partner Organisations 2014.

The adsorption complex of hydrogen chloride on copper-modified ZSM-5 was studied by FTIR and theoretical calculations. The results indicate that the Cl atom of hydrogen chloride is bound to the Cu cations when adsorbed at low pressures (<1 µbar). At higher pressures, HCl adsorbs on the zeolite Brønsted acid sites as well as is hydrogen bonded to the Cu in a larger cluster. Using in situ infrared spectroscopy, we observed a sharp decrease in stretching vibrational frequency of HCl of about 700 cm-1 compared with the H-Cl stretching vibration of gaseous hydrochloric acid. The findings were supported by density functional theory cluster quantum chemical calculations. © 2013 American Chemical Society.