Deactivation of palladium catalyst in catalytic combustion of methane

Abstract Catalytic combustion of natural gas, for applications such as gas turbines, can reduce NOx emissions. Palladium-on-stabilised alumina has been found to be the most efficient catalyst for the complete oxidation of methane to carbon dioxide and water. However, its poor durability is considered to be an obstruction for the development of catalytic combustion. This work was aimed at identifying the origin of this deactivation: metal sintering, support sintering, transformation PdO → Pd + 1 2 O 2 or coking. Catalytic combustion of methane was studied in a 15 mm i.d. and 50 mm length lab reactor and in a 25 mm i.d. pilot test rig on monolithic honeycomb substrates. Experiments were performed at GHSV of 50 000 h−1 in lab test and 500 000 h−1 in pilot test. The catalysts used were palladium on different supports on cordierite substrate. The catalysts were characterised by XRD, STEM, ATG and XPS. In steady-state conditions, deactivation has been found to be dependent on the air/methane ratio, the palladium content on the washcoat and the amount of washcoat on the substrate. An oscillating behaviour of the methane conversion was even observed under specific conditions, due to the reducibility of palladium oxide PdO to Pd. The influence of the nature of the support on the catalyst deactivation was also investigated. It has been shown that some supports can surprisingly eliminate this oscillating behaviour. However, in pilot test, deactivation was found to be very rapid, even with stabilised alumina supports. Furthermore, successive tests performed on the same catalyst revealed that the activity (light-off temperature, conversion) falls strongly from one test to another. Then, the stabilised alumina support was calcined at 1230°C for 16 h prior to its impregnation by palladium, in order to rule out its sintering. Experiments carried out on precalcined catalysts point out that deactivation is mostly correlated to the metal transformation under reaction conditions: activity decreases gradually as PdO sinters, but it dropped much more steeply in relation to appearance of metallic palladium.

[1]  J. Church,et al.  Stabilisation of aluminas by rare earth and alkaline earth ions , 1993 .

[2]  J. G. McCarty,et al.  Dispersion of palladium on alumina surfaces , 1994 .

[3]  E. Garbowski,et al.  Stabilization of alumina by addition of lanthanum , 1991 .

[4]  D. Trimm,et al.  Catalytic combustion of methane , 1995 .

[5]  Toshio Matsuhisa,et al.  Development of a high-temperature combustion catalyst system and prototype catalytic combustor turbine test results , 1995 .

[6]  M. Yamada,et al.  Development of a hybrid catalytic combustor for a 1300°C class gas turbine , 1995 .

[7]  H. Arai,et al.  Thermal stabilization of catalyst supports and their application to high-temperature catalytic combustion , 1996 .

[8]  L. Quick,et al.  Catalytic combustion reactor design and test results , 1995 .

[9]  Robert J. Farrauto,et al.  Catalytic chemistry of supported palladium for combustion of methane , 1992 .

[10]  H. Arai,et al.  Recent progress in high-temperature catalytic combustion , 1991 .

[11]  S. Järås,et al.  Catalytic Materials for High-Temperature Combustion , 1993 .

[12]  J. Geus,et al.  Sintering of pseudo-boehmite and γ-Al2O3 , 1991 .

[13]  M. Kerzhentsev,et al.  Catalytic Fuel Combustion—A Way of Reducing Emission of Nitrogen Oxides , 1990 .

[14]  D. Trimm.  Catalytic combustion (review) , 1983 .

[15]  M. Pijolat,et al.  Influence of surface area and additives on the thermal stability of transition alumina catalyst supports. II: Kinetic model and interpretation , 1987 .

[16]  H. Arai,et al.  Research and development on high temperature catalytic combustion , 1995 .

[17]  E. Ruckenstein,et al.  Role of interfacial phenomena in the behavior of alumina-supported palladium crystallites in oxygen , 1981 .

[18]  Robert Burch,et al.  Low NOx options in catalytic combustion and emission control , 1996 .

[19]  Akio Ohkoshi,et al.  Hybrid Catalytic Combustion for Stationary Gas Turbine Concept and Small Scale Test Results , 1987 .

[20]  H. Schaper,et al.  The influence of lanthanum oxide on the thermal stability of gamma alumina catalyst supports , 1983 .

[21]  Robert J. Farrauto,et al.  Thermal decomposition and reformation of PdO catalysts; support effects , 1995 .