Impregnated Ni/ZrO2 and Pt/ZrO2 catalysts in dry reforming of methane: Activity tests in excess methane and mechanistic studies with labeled (CO2)-C-13

摘要

In the present work, 1%Ni/ZrO2, 3%Ni/ZrO2 and 1%Pt/ZrO2 catalysts prepared by impregnation with the concomitant addition of NaHCO3 were investigated and compared by structural investigations such as TEM, XRD, TPR, XPS and DRIFTS methods. Temperature programmed dry reforming (DRM) experiments were done (i) at atmospheric pressure in plug flow reactor and an in situ DRIFTS cell or (ii) under sub atmospheric pressure (similar to 50 mbar) in a closed loop circulation system using labelled (CO2)-C-13 to trace the fate of carbon compounds. The calcined and reduced fresh catalysts contained nanoparticles in the range of 2-18 nm. According to the TPR results, in 3%Ni/ZrO2 catalyst most of Ni is in strong interaction with the support. The presence of sodium was suggested to induce the appearance of strongly bound bridged CO sites during CO chemisorption in DRIFTS measurements for all samples and to cause BE shift in XPS spectrum of the highly dispersed Pt/ZrO2 only. In the catalytic tests in plug flow reactor the 3 wt%Ni/ZrO2 sample turned to be the most active catalyst, but coke was deposited on its surface measured by the subsequent temperature programmed oxidation (TPO) measurements. In situ low temperature DRIFTS-DRM measurements suggested that stability of surface carbonates is less when dispersed electron-rich Pt nanoparticles are on the ZrO2 support, while more carbonates accumulate on Ni/ZrO2 samples. Based on our isotope labeled (CO2)-C-13+(CH4)-C-12 experiments in circulation system, the same initial reaction pathways could be suggested for the Ni and Pt catalysts. The reactive surface carbon species from the two different sources (CH4 and CO2) were completely scrambled on 3 wt%Ni/ZrO2 at 600 degrees C, suggesting that common reaction intermediates do exist. (C) 2015 Elsevier B.V. All rights reserved.