Solution combustion synthesized porous ceria-zirconia supported platinum-ruthenium catalyst for simultaneous oxidation of propane and carbon monoxide

Abstract

The development of catalysts for enhanced catalytic conversion of carbon monoxide and volatile organic compounds such as light hydrocarbons, into clean products of carbon dioxide and water, is crucial for environmental pollution control. An ideal catalyst should be able to achieve low conversion temperatures, while maintain high thermal stability and consistency in catalytic performance over prolonged cycling. Catalyst design through composition and morphology control in the synthetic steps is crucial to obtain a product with targeted performance. Various investigations of metal/ metal oxide catalysts for catalytic conversion of common air pollutants have been reported in the literature. However, there were limited studies in the durability and thermal stability of the catalyst through accelerated ageing and extended cycling. This restricts the practical applicability of such investigations, and there has been little breakthrough in the commercialization of new catalysts and deployment of novel synthesis methods in industry. The objective of this research is to develop a porous bifunctional catalyst that is durable, thermally stable, and active towards low temperature simultaneous oxidation of propane and carbon monoxide.

In this work, a platinum-ruthenium doped ceria-zirconia catalyst has been developed by first utilizing solution combustion synthesis to produce porous ceria-zirconia as the metal oxide support, followed by doping of platinum and ruthenium by incipient wetness impregnation. The mixture is subjected to subsequent reduction using sodium borohydride to form metallic platinum and ruthenium phases in the ceria-zirconia structure. The resulting platinum-ruthenium doped ceria-zirconia catalyst has a porous structure with high surface area (48 m2/g) and high pore volume (0.19 cm3/g), which provides additional catalytic active sites for the reaction to occur, and more pathways for reaction gas to penetrate through the catalyst’s microstructure.

The as-synthesized platinum-ruthenium doped ceria-zirconia catalyst demonstrates excellent catalytic activity towards propane oxidation; its performance is unaffected in the presence of carbon monoxide. With the enhanced porous structure achieved through solution combustion synthesis, coupled with doping 0.5 wt.% platinum and 0.5 wt.% ruthenium, it acts as an effective dual catalyst for simultaneous propane and carbon monoxide oxidation. It achieves 50% propane conversion at 210 °C, 95 % propane conversion at 261 °C, and 100 % carbon monoxide conversion simultaneously at 201 °C, even after accelerated thermal ageing at 1000 °C for 24 hours. In the extended cycling performance tests (11 cycles), the aged catalyst is durable over repeated cycling, consistently achieving 90 % propane conversion at 250 ºC, and full (100 %) propane conversion at 300 ºC. For simultaneous carbon monoxide oxidation, full (100 %) conversion is consistently achieved at 210 ºC in the extended cycling test. The oxidation of both propane and carbon monoxide are complete and fully selective to formation of carbon dioxide. There is no side product detected. The synthesis of platinum-ruthenium doped ceria-zirconia outlined in this work exemplifies a rapid, scalable and tuneable synthesis method that can be utilized to produce mixed metal oxide supported bimetallic or multimetallic catalysts with enhanced porosity, for application in catalytic oxidation reactions.