On the Interaction between CO and a Coke-Resistant NiIn/SiO2 Methane Dry Reforming Catalyst: a DRIFTS and CO Pulse Study

Recently a new In-promoted Ni catalyst has been elaborated and published in our laboratory, that has beneficial properties in dry reforming of methane, including inhibited coking. In order to get deeper insights into the coke-free behavior of this SiO2-supported 3 wt % Ni 2 wt % In catalyst, we wished to monitor the interaction between CO and the catalyst. For this purpose DRIFTS studies under CO, CO2, or CO2 + CH4 flow at different temperatures and CO pulse flow experiments at 600 degrees C followed by mass spectrometry were carried out. A linear carbonyl band at 2013 cm(-1) in the DRIFT spectra of the In-promoted catalyst was attributed to CO bonded on Ni atoms surrounded by In neighbors. The lack of bridge and multicoordinated carbonyls also proved the dilution of Ni surface with In. In the presence of a CH4:CO2 = 70:30 dry reforming mixture, stable Ni bonded CO species were found on NiIn/SiO2, suggesting that the metallic sites remained clean during the reaction (unlike on the reference Ni/SiO2). At the end of the reforming reaction, little surface segregation of the original bimetallic particles and the formation of islands with adjacent Ni sites were presumed based on the DRIFTS results. The pulse CO experiments at 600 degrees C, tailored to detect the most sensitive surface sites for Boudouard reaction, proved that CO dissociation on the bimetallic catalyst was markedly hindered, while it caused carbon deposition on the unpromoted sample. Based on all these results, we postulate a picture of the working catalyst that is dispersed ensembles of NiIn-InOx entities stabilized by SiO2.