Identification of the Active Sites for CO and C₃H₈ Total Oxidation over Nanostructured CuO−CeO₂ and Co₃O₄−CeO₂ Catalysts

Abstract

Nanostructured Co 3 O 4 -CeO 2 and CuO-CeO 2 catalysts with the specific surface areas exceeding 100 m 2 g -1 were synthesized by a surfactant-templated method. The catalytic performance of these catalysts was investigated using the total oxidation of CO and C 3 H 8 as model reactions. The results show that the Co 3 O 4 -CeO 2 catalysts are less active for CO oxidation but are more active for C 3 H 8 oxidation as compared with the CuO-CeO 2 catalysts. Moreover, the Co 3 O 4 -CeO 2 catalysts exhibit a volcano-type performance for CO oxidation with the cobalt content increasing. The in situ diffuse reflectance infrared spectroscopy (DRIFTS) study shows that CO is adsorbed mainly as carbonyl (2106 cm -1 ) and bidentate carbonate (1568 and 1281 cm -1 ) on CuO-CeO 2 , and only as bidentate carbonate (1591 and 1268 cm -1 ) on Co 3 O 4 -CeO 2 . On the basis of the results of structural characterization, redox properties, and in situ DRIFTS study, the active sites for CO and C 3 H 8 oxidation are identified, respectively. Carbon monoxide oxidation preferentially occurs at the interface between CeO 2 and CuO or Co 3 O 4 , whereas propane oxidation takes place on the neighboring surface lattice oxygen sites in CuO or Co 3 O 4 crystallites. The different requirements of the active sites are determined by the different reaction mechanisms and the rate-determining steps. It is also found that the introduction of a small amount of Pd to Co 3 O 4 -CeO 2 can remarkably promote the CO oxidation activity, but it hardly enhanced the C 3 H 8 oxidation activity of the catalyst. The different reaction mechanisms, on molecular level, are identified and discussed in detail.

Highly dispersed Pd on macroporous SmMn2O5 mullite for low temperature oxidation of CO and C3H8

“…since the lattice oxygen of mullite might be shared with Pd species, contributing to the variation of the peak at 665 cm À1 as well. 36,37 Thus variation might affect the activity of lattice oxygen.…”

“…[57][58][59] In addition, the enhanced activity of oxygen species (certied by CO + O 2 pulse hereaer) contributes as well. 28,37 As the Pd dispersion is higher for the Pd/SMO-EG&M compared with other samples, its surface Pd site was highly exposed and could be reduced easier. The lower temperature suggests higher reducibility of the Pd/SMO-EG&M in the whole range, suggesting that the reduction of mobile oxygen and surface adsorbed oxygen species is more facile.…”

“…Most of active sites for CO oxidation are at the interface between transition metal oxide and the supported species where spilled oxygen are transmitted via support. 1,36,37 In this way, the oxygen species of PdO x on EG&M support could be motivated at lower temperatures and spilled to the surface of catalyst, and such activated oxygen atom could preferentially react with the adsorbed CO and form bidentate carbonate via spillover, giving rise to the improved catalytic performance. Moreover, due to a larger number of exposed Pd sites, the Pd/SMO-EG&M is benecial to CO chemisorption (Fig.…”

Co3O4 particles grown over nanocrystalline CeO2: influence of precipitation agents and calcination temperature on the catalytic activity for methane oxidation

“…High bulk oxygen mobility (through the Mars-van Krevelen mechanism) and formation of highly active oxygen species activated by oxygen vacancies are widely recognized as the main factors influencing the catalytic activity of 44 However, more commonly the reduction of Co 3 O 4 is described as a two-step process involving the intermediate reduction of CoO. 42 These different results could be explained by considering that the reduction behaviour of Co 3 O 4 is highly dependent on the preparation method and dispersion of the particles.…”

Co3O4@CeO2 Core@Shell Cubes: Designed Synthesis and Optimization of Catalytic Properties

“…It is accepted that the CO oxidation process takes place at the interface between the CeO 2 and Co 3 O 4 components. [24] Therefore, increasing the interfacial area of CeO 2 -Co 3 O 4 HNs may be a feasible way to improve their catalytic performances. One way to optimize the fraction of the interfacial area of the two components is to prepare core@ shell structures.…”