Professor Michael Stockenhuber

© 2018 American Chemical Society. Catalysts of iron oxide on ¿-alumina and silica which were prepared by an incipient wetness impregnation technique have been investigated in an effort to understand how the surface chemical properties are influenced by the nature of the supports. Surprisingly, this is the first study to compare in depth the influence of the supports on physicochemical parameters such as acidity, site nuclearity, and reducibility. In this study, surface characterisation techniques including N2physisorption at -196 °C, ammonia temperature-programmed desorption, inductively coupled plasma optical emission spectrometry, temperature-programmed reduction with hydrogen, CO-chemisorption, scanning electron microscopy, transmission electron microscopy, and NO adsorption by in situ Fourier transform infrared spectroscopy have been performed to understand the different surface reactions occurring over the two different supports. The aim of this study is to ascertain the primary differences between these two catalysts using several catalyst characterization techniques and correlate their chemical and structural differences to their catalytic activity in the conversion of 2-chlorophenol. The results disclose a higher density of acid sites, a smaller particle size of iron oxide, stabilization of Fe(II) aluminate after reduction on the alumina surface, and finally, the formation of isolated iron cations on the surface of alumina which are notably absent on the silica-supported catalyst.

© 2018 American Chemical Society. This paper describes an alternative process for chloroform decomposition via nonthermal plasma polymerization at atmospheric pressure and investigates the effect of methane and hydrogen addition on the process. The effect of both additives was assessed separately, where experiments were conducted in a double dielectric barrier discharge reactor under nonoxidative conditions. The most profound impact of the additives was a significant increase in the yield of non-cross-linked polymer produced compared to that in their absence. The addition of methane resulted in a 120% increase in polymer yield, while in hydrogen the increase was 31%. Critical parameters such as effect of the methane and hydrogen concentration on the conversion of chloroform at various applied voltages, the product distribution, mass balance, and polymer characterization are elucidated in this paper. Single pass conversions of 61% and 68% (with corresponding mass balances of 98% and 95%, respectively) were achieved for CHCl3+ CH4and CHCl3+ H2feed scenarios, respectively. Furthermore, a polymerization mechanism which explains the formation of major chain structures as well as structural defects in the polymer is expounded upon in the paper.

© 2018. Mechanisms of pyrolysis of several representative cyclodiene pesticides, viz., dieldrin, aldrin and isodrin, have been studied by quantum chemical techniques and dieldrin and isodrin have been subjected to experimental pyrolysis investigation. Comparison is made with earlier studies on another cyclodiene - endosulfan. Cyclodienes which are initially produced by Diels-Alder condensation of hexachlorocyclopentadiene (HCCP) and a substrate, initially decompose by retro Diels-Alder reaction back into HCCP and the substrate, both of which undergo further reaction. In the case of dieldrin, pyrolysis is initiated at 673 K and the substrate, norbornadiene oxide, further decomposes to produce CO and benzene which are observed experimentally. Above ~800 K hexachlorocyclopentadiene undergoes rapid Cl bond fission and Cl atoms abstract H atoms from dieldrin forming HCl and lead to four different types of dieldrin radicals, just one of which can undergo a sequence of reactions of modest energy barriers to lead to the major observed high temperature products, pentachlorostyrene, hexachlorostyrene and polychlorinated benzenes. In contrast to other cyclodienes, pyrolysis of isodrin which is initially produced by Diels-Alder condensation of hexachloronorbornadiene and cyclopentadiene does not undergo initial retro Diels-Alder decomposition, instead undergoing an intramolecular rearrangement to a "birdcage" structure which eventually decomposes to HCl and aromatic soot precursors. A simple relationship between the rate constants for retro Diels-Alder decomposition and Cl fission of HCCP is discussed to evaluate whether cyclodiene-contaminated soils might be remediated via thermal desorption.

© 2018 American Chemical Society. Catalytic combustion of ventilation air methane (VAM) is a potential solution for abatement of this greenhouse gas. In this study, we evaluate the combustion of VAM (with methane concentrations below 1%) spanning over 100 h time on stream (TOS) during reaction over a Pd/HZSM-5 catalyst. The aim is to understand the structural changes that lead to catalyst deactivation. We observe the formation of carbonaceous deposits even under oxygen rich conditions which are an important contributor to deactivation. X-Ray absorption spectroscopic (XAS) investigation shows that, in addition to carbon deposits, the growth of Pd oxide clusters leading to a reduced number of accessible sites and in turn intrinsic activity. STEM-EDS analysis disclosed the presence of the carbonaceous deposit on the surface of the used catalyst, and TGA confirmed the presence of different carbon species on the used catalyst under very lean conditions. Structural changes show that Pd-O / acid-base interactions have a significant influence on the structure of the active site. This assertion is consistent with findings from acid-base characterisation experiments. Although the catalyst displayed a high level of stability over the first 10 h of VAM combustion, long-term reaction, in the presence of water vapour, is associated with a partial rearrangement of the zeolite, accompanied with a gradual deactivation of the catalyst. This rearrangement is associated with a decrease in surface area and pore volume which is consistent with the significant changes observed in the Al-X-Ray absorption near-edge spectroscopic (XANES) analysis. A comparison of the NH3-TPD of fresh and used Pd/HZSM-5 catalysts shows that the strength of the acid sites are significantly reduced. This is a consequence of the changing nature of transition metal interaction with the zeolite which is accompanied by the dealumination of the zeolite support, thereby enhancing Pd agglomeration and the emergence of two low index surface orientation facet planes identified as PdO (101) and PdO (100). A higher turnover frequency (TOF) (0.031 s-1) for reactivated Pd/HZSM-5 after removing all carbonaceous material compared to TOF (0.024 s-1) for used Pd/HZSM-5 was observed. The catalyst regained 75% of its initial catalytic activity after removing carbonaceous compound from the used catalyst. We propose the formation of palladium carbonaceous complex manifesting itself in carbonate and carbonyl group observed in used Pd/HZSM-5. These species act as an important contributor to catalyst deactivation and cause partial reversible deactivation during long-term VAM combustion.

© 2016 Elsevier B.V. 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 CHCl3and C2HCl3are 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.

� 2015 Elsevier Ltd. 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.

© the Owner Societies 2016. 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/Al2O3catalyst 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.

© 2016 Elsevier B.V. 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 CDCl3and 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.

© 2015 The Institution of Chemical Engineers. 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 H<inf>2</inf>:CO ratios depending on the hydrocarbon used. This paper examines the effect of varying the H<inf>2</inf>:CO ratio with respect to C<inf>1</inf> to C<inf>4</inf> 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 H<inf>2</inf>: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.

© 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.