Environmental Catalysis

Baiker's significant contributions to environmental catalysis are in the fields: selective catalytic reduction of nitrogen oxides (SCR), oxidation of carbon monoxide, synthesis of chemicals from CO2, partial oxidation, coupling and combustion of methane, and lean- burn engine and hybrid engine exhaust catalysis. Studies on the selective catalytic reduction of NOx [2.a] are focused on the mechanism and on the surface structure of the vanadia, molybdena and chromia based catalysts used for this reaction. Using in-situ diffuse reflectance spectroscopy combined with mass spectroscopy and thermal desorption, the surface sites relevant for SCR were uncovered. With vanadia-based catalysts, the SCR activity was found to depend on the fraction of Brønsted-bound ammonia, which correlates with the vanadia surface concentration. To investigate the kinetics of SCR at very low reactant concentration  (10-9 ppm), positron-13NO molecules produced with a cyclotron were used. The measuring technique based on this short-lived radio active isotopes expands the accessible range of reactants by more than 11 orders of magnitude, and so opens the possibility of studying surface reaction kinetics in a totally new concentration regime. The understanding of the structure sensitivity of SCR observed over vanadia and chromia based SCR-catalysts has let to structurally optimized SCR catalysts based on vanadia and amorphous chromia.  The Baiker group has significantly contributed to the heterogeneously-catalyzed transformation of carbon dioxide to valuable products [2.b]. They were among the first who found suitable catalysts for converting carbon dioxide to methanol. Various aspects of the mechanism of this reaction were uncovered using in-situ vibrational spectroscopy and other techniques. The gained information together with the knowledge on amination reactions existing in the group, has led to the direct catalytic synthesis of aliphatic amines starting from CO2, NH3 and H2. Later the potential of carbon dioxide as a C1 building block in chemical synthesis has been demonstrated on various examples, including formylation of amines and the synthesis of organic carbonates. Studies on the oxidation of carbon monoxide [2.c] have led to structurally and chemically optimized CO oxidation catalysts useful for low temperature applications. Research on the partial oxidation of methane [2.d] revealed the relevance of surface and gas phase reactions for the selectivity to methanol. Palladium/zirconia catalysts highly active for methane combustion and selective for the production of synthesis gas were prepared by in-situ activation of glassy palladium zirconium alloys. In the field of auto exhaust catalysis [2.e], the Baiker group discovered that several catalysts including Cu-ZSM-5 and alumina-based catalysts, which have been suggested to be suitable for lean burn- and diesel engine exhausts, can produce significant amounts of harmful HCN and HNCO. The formation of this harmful species has been overlooked by previous investigators dealing with these catalyst systems. Iridium-based catalyst were shown to possess interesting potential for auto exhaust catalysis. Present work focuses on NOx  storage reduction (NSR) catalysts [2.f]. Very recently a systematic study revealed that various Ba-containing species exist on the Pt-Ba/Al2O3 surface that show different efficiency in NOx storage. The control of the population of these Ba-species was found to be essential for optimal storage behaviour. Baiker's group was among the first  who  explored  catalysis  of  exhausts  of  hybrid  drive  systems  [2.g]. Experimental studies of the dynamic behaviour of catalysts combined with modelling provided the basis for the design of catalytic converters suitable for this application.

[2.a]     Use of Positron Emitting 13N for Studies of the Selective Reduction of NO by NH3 over Vanadia/Titania Catalyst at Extremely Low Reactant Concentrations, U. Baltensperger. M. Amman, U. Borchert, B. Eichler, H.W. Gäggeler, D.T. Jost, J. A. Kovacs, A. Türler, U. W. Scherrrer, and A. Baiker, J. Phys. Chem., 97, 12325 (1993).

In-Situ Diffuse Reflectance FTIR Study of Selective Catalytic Reduction of NO with NH3 over Vanadia/Titania Aerogels, H. Schneider, S. Tschudin, M. Schneider, A. Wokaun, and A. Baiker, J. Catal., 147, 5 (1994).

[2.b] Hydrogenation of Carbon Dioxide over Copper-Zirconia Catalyst Prepared by In Situ Activation of Amorphous Copper-Zirconium Alloy, D. Gasser, and A. Baiker, Appl. Catal., 48, 279 (1989).

Ruthenium-Catalyzed Formylation of Amines with Dense Carbon Dioxide as C1- Source, L. Schmid, A. Canonica and A. Baiker, Appl. Catal. A, 255, 23 (2003).

[2.c] CO Oxidation over Au/ZrO2 Catalysts: Activity, Deactivation Behavior, and Reaction Mechanism, A. Knell, P. Barnickel, A. Baiker, and A. Wokaun, J. Catal., 137, 306 (1992).

Gold/Titania Interfaces and Their Role in Carbon Monoxide Oxidation, J.D. Grunwaldt and A. Baiker, J. Phys. Chem. B, 103 (6), 1002 (1999).

[2.d] Partial Oxidation of Methane: The Role of Surface Reactions, F.J. Thomas, and A. Baiker, Ind. Eng. Chem. Res., 31, 2272 (1992).

Methane Oxidation over Palladium on Zirconia Prepared from Amorphous Pd1Zr3 Alloys, P. Marti, M. Maciejewski and A. Baiker, J. Catal., 139, 494 (1993).

[2.e] Hydrogen Cyanide Formation in Selective Reduction of Nitrogen Oxides by Hydrocarbons over Cu-ZSM 5 Catalyst, F. Radtke, R.A. Köppel and A. Baiker, Appl. Catal. A, General, 107, L125 (1994).

Structure Sensitivity of NO Reduction over Iridium Catalysts in HC-SCR, C. Wögerbauer, M. Maciejewski and A. Baiker, J. Catal., 205, 157 (2002).

[2.f]     Pt-Ba/Alumina NOx Storage-Reduction Catalysts: Influence of Barium Loading on Build-Up, Stability and Reactivity of Ba-Containing Phases,  M. Piacentini, M. Maciejewski and A. Baiker, Appl. Catal. B., 59, 187 (2005).

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