Methane reforming over Ni-based pyrochlore catalyst: deactivation studies for different reactions

Abstract

A 1 wt% Ni-based La2Zr2O7 pyrochlore catalyst was synthesized using the modified Pechini method. The catalyst was characterized by H2-TPR, and pre- and post-reaction XRD, and tested for its methane-reforming activity under three different reaction conditions: (a) dry-reforming (CH4 + CO2), (b) oxy-CO2 reforming (CH4 + CO2 + O2), and (c) bi-reforming (CH4 + CO2 + H2O). The TPR results show that NiO in the fresh, calcined catalyst is completely reversible to Ni0. The XRD results show that the crystalline pyrochlore structure is stable under all three reaction conditions. Under dry-reforming conditions, the catalyst deactivated rapidly. In oxy-reforming, the catalyst activity also decreased, but far less rapidly than under dry-reforming conditions. However, under bi-reforming conditions, no deactivation was observed at comparable times-on-stream. TPO of the spent catalysts showed greatest carbon deposition for the dry-reforming, a significant portion of which was graphitic and difficult to remove. For oxy-reforming, there was much less carbon deposition as compared to the dry-reforming, and a major part of which was the amorphous, atomic carbon, which is relatively easy to remove. Unlike under bi-reforming, no significant carbon deposition was observed at the conditions tested here. This indicates that the presence of steam resists carbon deposition compared to dry-reforming or oxy-reforming.