NiO/CeO2-Sm2O3 nanocomposites for partial oxidation of methane: In-situ experiments by dispersive X-ray absorption spectroscopy

L. M. TOSCANI; M. BELLORA; HUCK-IRIART, CRISTIÁN; SOLDATI, ANALÍA L.; SACANELL, JOAQUÍN; MARTINS, TEREZA S.; ALDO F. CRAIEVICH; MARCIA C. A. FANTINI; S.A. LARRONDO.; D.G. LAMAS

Encuentro; 31st RAU Annual Users Meeting; 2021

CeO2-based materials are being extensively used for catalytic and electrocatalytic applications due to their redoxproperties. In particular, the addition of a metallic phase such as Ni to CeO2-based catalysts for methane oxidation hasbeen widely recognized to increase Ce reducibility by the presence of a strong metal-support interaction. However, itremains unclear if boosting Ce reducibility promotes a direct increase in catalytic activity for partial oxidation ofmethane. In this context, the role of sample nanostructure in the redox behavior of NiO/CeO2-Sm2O3 (NiO/SDC)samples is of key interest to understand CH4 activation, particularly, in terms of (i) the interaction between metallicand ceramic phases, (ii) the effect of the average crystallite sizes of both phases in catalytic activity, and (iii) theconcentration of reduced species in the surface of the catalyst. In order to study samples with different averagecrystallite sizes and specific surface areas, and potentially different redox behavior, SDC and NiO/SDCnanocomposites submitted to different calcination temperatures, from 400 ℃ up to 1100 ℃, were prepared. In this work, we analyze the sample reducibility and catalytic activity for partial oxidation of methane. We assess the role of the average crystallite size and specific surface area in Ni and Ce reduction kinetics by studying diluted H2 and CH4/O2 mixtures by in-situ dispersive X-ray absorption spectroscopy experiments with synchrotron radiation. Our results indicate that the average crystallite size and surface area play a key role in CH4 activation through modification of the sample redox behavior [1]. The oxidation of the metallic phase is the main cause of sampledeactivation, revealing a clear relationship between the temperature of maximum Ni oxidation rate and grain size. An interplay between Ce atoms from the support and Ni from the active phase was observed during the experiments, evidencing that a high Ce3+ content in catalyst support is detrimental to catalytic activity.