In Situ Surface Chemistries and Catalytic Performances of Ceria Doped with Palladium, Platinum, and Rhodium in Methane Partial Oxidation for the Production of Syngas

Abstract

Methane partial oxidation (MPO) chemically transforms natural gas into syngas for the production of gasoline. CeO2 doped with transition-metal ions is one type of catalyst active for MPO. A fundamental understanding of MPO on this type of catalyst is important for the development of catalysts with high activity and selectivity for this process. CeO2-based catalysts, including Pd-CeO2-air, Pd-CeO2-H2, Pt-CeO2-air, Pt-CeO2-H2, Rh-CeO2-air, and Rh-CeO2-H2, were synthesized through doping noble-metal ions in the synthesis of CeO2 nanoparticles. The catalytic activity and selectivity in the production of H2 and CO through MPO on these ceria-based catalysts as well as their surface chemistries during catalysis were investigated. They exhibit quite different catalytic performances in MPO under identical catalytic conditions. In situ studies of their surface chemistries during catalysis, using ambient-pressure X-ray photoelectron spectroscopy (AP–XPS), revealed quite different surface chemistries during catalysis. Correlations between the catalytic performances of these catalysts and their corresponding surface chemistries during catalysis were developed. Differing from the other four catalysts, Rh doped in the surface lattice of a CeO2 catalyst, including Rh-CeO2-air and Rh-CeO2-H2, is in a complete ionic state during catalysis. Correlations between the in situ surface chemistry and the corresponding catalytic performance show that Rh ions and Pt ions doped in the lattice of CeO2 as well as metallic Pd nanoparticles supported on CeO2 are active components for MPO. Among these catalysts, Rh-doped CeO2 exhibited the highest catalytic activity and selectivity in MPO.

Understanding complete oxidation of methane on spinel oxides at a molecular level

“…To avoid surface charging, we use Au, Ag, or HOPG to load catalysts for AP-XPS studies and control the thickness of catalyst layer on a surface 19,37,38 .…”

Utilization of Volatile Organic Compounds as an Alternative for Destructive Abatement

“…Among them, Rh based catalysts were found to be most active and stable and widely reported in scientific literature ( Table 3). As reported earlier, noble metals are highly selective for oxidation reactions due to high O2 adsorption and resistance against carbon formation [69]. POM is thermodynamically an exothermic reaction, but most of the catalysts are active and selective at higher temperatures 700-1000 °C (shown in Table 3).…”

Evolution of surface of Pd-Rh bimetallic nanocubes and its correlation with CO oxidation

“…The in-situ characterization of surface chemistry of Pd-Rh bimetallic catalysts during catalysis was performed with AP-XPS [32][33][34][35][36][37][38][39]. Monochromated Al Kα line is used as X-ray source.…”

“…An average of the pressures at entrance and exit is defined to be the pressure above the catalyst in the reaction cell. More detailed description of the AP-XPS system can be found in the previous publications [32][33][34][35][36][37][38][39].…”