Platinum Metals Rev., 2003, 47, (1), 13
Catalyst Life Cycle Conference
The Catalyst Life Cycle conference, held at the University of Bath on 16—17th September, 2002, was a joint meeting of the UK’s Royal Society of Chemistry and Institution of Chemical Engineers under their subject groups of SURCAT, Process Technology and Applied Catalysis. This is a biannual thematic meeting, with a previous one in Edinburgh being on kinetics and in situ methods in heterogeneous catalysis. Approximately 75 participants, mostly from U.K. universities and industry, attended the conference. There were 16 oral presentations — half of which were concerned with the platinum group metals (pgms) – and a number of poster presentations. As expected from the sponsoring groups, the talks provided an interesting combination of applied catalysis and more fundamental catalytic chemistry on the microreactor scale. With the conference subtitle of ‘Preparation, Activation, Deactivation and Regeneration’, most talks focused on catalyst deactivation/regeneration and covered such diverse areas as large scale industrial reactions (for example, catalytic combustion and partial oxidation), automotive catalysis, fuel cells and fine chemical synthesis.
The opening invited lecture by John Birtill (consultant, U.K) was entitled “But will it last until the shutdown?’. This presentation introduced techniques for interpreting and predicting the effects of catalyst decay in industrial process catalysis. Kinetic expressions for describing catalyst decay and possible approaches for determining the mechanism of decay were discussed.
From the industrial plant scale the talks moved to the nanoscale with Mike Bowker (University of Reading, U.K) describing scanning tunnelling microscopy studies of model supported-catalysts. Atomic scale processes can be observed for pgms (Rh and Pd) deposited in situ on TiO2 single crystals in ultra high vacuum conditions. Effects such as spillover of chemisorbed oxygen, encapsulation under oxidising conditions and compound formation between metal and the reduced support were demonstrated.
The second invited lecture, gjven by Pierre Gallezot (CNRS, Villeurbanne, France), was on the stability of platinum metal catalysts in the liquid phase hydrogenation and oxidation of organic compounds. He began by outlining the main causes of catalyst deactivation: sintering, leaching and poisoning by strongly adsorbed species. One example he described was the hydrogenation of glucose to sorbitol which is used in the food and pharmaceutical industries. This reaction is usually performed with a Raney Ni catalyst which deactivates by leaching of the metal promoter. An alternative catalyst that can be used is ruthenium (Ru) on activated carbon. This has higher activity, especially when platinum (Pt) is added, and gives extremely high conversion/selectivity and higher stability than the Ni catalyst. A second example described was the total oxidation of organic pollutants in water. This uses a Ru/TiO2 catalyst which provides advantages over homogeneous catalyst alternatives such as Cu salts, which are efficient but have issues associated with catalyst recovery.
The third and final invited lecture was by Malcolm Green (University of Oxford, U.K) who discussed new catalysts for the conversion of methane (CH4) to liquid hydrocarbons. Besides looking at catalysts for syngas production from CH4, he demonstrated the performance of a new Co-based catalyst for Fischer Tropsch synthesis suggesting that gas to liquid technology would become increasingly important in the near future as oil reserves are depleted.
David Jackson (University of Glasgow, U.K) presented work on butane dehydrogenation over a Pt/Al2O3 catalyst using a pulsed flow microreactor. Changes in product formation and carbonaceous residue were observed for sequential pulses of butane for different catalyst pretreatments. The first pulse produced no butene but only CH4 and carbonaceous residue. With subsequent pulses of butane the build up of the carbonaceous deposit increased and the selectivity to butene also increased.
Jenny Jones (University of Leeds, U.K.) presented work on sulfur poisoning of CH4 combustion catalysed by Pt, Pd and Rh. Sulfur compounds, such as mercaptans, are used as odorants in domestic supplies of natural gas, so the effects of a range of sulfur compounds on catalyst deactivation were studied. Catalysts used were 2 wt.% Pd, Pt and Rh on alumina with a gas feed of 4% CH4 in air. Activity was found to increase in the order: Pt < Rh < Pd. TEM helped to distinguish between sulfur-induced agglomeration and simple site blocking effects in catalyst deactivation.
The final session contained three presentations on automotive catalysis. The first two were concerned with NOx storage/reduction (NSR) catalysts for NOx control in lean-burn engines. These catalysts consist of a Pt/Ba component which stores NOx as nitrate during lean engine operation. The engine periodically runs rich and under this condition the nitrate is decomposed and the released NOx is reduced with the help of a Rh component in the catalyst. David James (University of Reading, U.K.) presented pulsed flow microreactor work on the effect of Pt loading on the decomposition of Ba(NO3)2 and the difference between using H2 or CO as the reductant. Pt was shown to promote nitrate decomposition with the extent of the promotion increasing with Pt loading. H2 was shown to be superior to CO in NOx reduction.
The second presentation on NSR catalysts was by Stephen Poulston (Johnson Matthey) who described the effects of gas composition on the regeneration of nitrated or sulfated model NOx storage catalysts consisting of Pt/Ba. Again the advantage of H2 over CO as a reductant was highlighted. The influence of CO2 in the simulated gas feed was also described. CO 2 is often omitted from synthetic exhaust feed compositions but has an effect on catalyst regeneration by lowering the temperature of Ba nitrate and sulfate decomposition.
The final talk by James Anderson (University of Dundee, U.K.) was on the use of an oxychlorination treatment to regenerate engine-aged three-way catalysts. Oxychlorination partially recovered catalyst activity and, in the case of Pd-based catalysts, also the oxygen storage capacity; there was some evidence for redispersion of Pt but not of Rh.
This short highly-directed conference provided an insight into many of the current themes of interest to catalyst scientists. Selected papers will be published in a special issue of Catalysis Today .
The next conference is expected to be a meeting to mark the retirement of Professor Geoff Webb on 16–18th July, 2003, at the University of Glasgow (http: //www.chem.gla.ac.uk/colloquia/catalyst/Catalysis_Symposium.html). For further information visit the websites at www.rsc.org and www.icheme.org.
Stephen Poulston is a Senior Scientist at the Johnson Matthey Technology Centre. His interests lie in automotive catalyst technology.
Steve Pollington is a Senior Scientist at the Johnson Matthey Technology Centre. He is interested in process catalysis and automotive catalyst technology.