We demonstrate that the kinetics of the Sabatier reaction catalysed by sorption catalysts depends on the nanostructure of the catalyst-sorbent system. The catalysts are prepared by ion exchange of a nickel nitrate solution in two zeolites with different pore sizes. Besides their different pore sizes - which enables or hinders the adsorption of the reactants, intermediates and products in the inner of the crystallites - the catalyst systems have slightly different size distributions of the Ni-particles. By studying various catalysts with different Ni-contents we can attribute different catalytic activity and in particular the shape selectivity of the zeolite support. Therefore we focus on the microstructural characterization of the catalyst. We observe that the selectivity for methane is greatly enhanced if the pore size of the support is larger than 5 angstrom, while pore sizes of less than 3 angstrom reduce the overall conversion rate and the selectivity for methane. Thus, Ni on 3A zeolites can be used as low temperature catalysts for the reversed water-gas shift reaction to produce carbon monoxide.