Effect of support acidity on coke removal in methane CO2 reforming

J. Ni, L. Chen, S. Kawi, J. Lin
Institute of Chemical and Engineering Sciences, Singapore, SG

Keywords: hydrogen production, methane CO2 reforming, methane dry reforming, support acidity, coke deactivation

Summary:

Methane CO2 reforming (MCR) produces 1:1 H2/CO suitable for Fischer-Tropsch synthesis. Nickel is the best catalyst for MCR, but coking is serious. The addition of B2O3 significantly influenced the activity and stability of the Ni/Al2O3 catalysts by changing the surport acidity. 5wt%Ni/Al2O3 catalysts with various B2O3 loading were prepared and characterised by XRD, CO2-TPD, NH3-TPD, in-situ DRIFTs for pyridine adsorption and MCR reaction. The Ni particle size increased slightly from 5.8 to 9.1 nm with increasing B2O3 content from 0 to 10wt%. However the addition of 1wt%B2O3 depleted all weak Lewis acid and basic Al-O-H sites, leaving only strong Lewis acid sites on Al2O3, the latter of which facilitated fast accumulation of carbon via CO2CO*C*. 5wt% B2O3 could generate weak acidic OH groups, in favor of carbon gasification by C* + OH à COH*  CO + H*. This catalyst performed better than other three catalysts. Addition of 10 wt% B2O3 resulted in Al4B2O9 overlayer and extra strong Lewis acid sites, leading to quick catalyst deactivation. The reaction mechanism over the supported Ni has been proposed, whereby nickel catalyzes CH4 and CO2 activation and decomposition, followed by O-H groups oxidizing surface CHx species.