Synchrotron PXRD deconvolutes nickel particle and support changes in Ni/ZrO$_{2}$ methanation catalysts

Understanding catalyst deactivation is important for future knowledge-based design of catalysts with improved stability. Deactivation by thermal aging is particularly relevant for exothermic reactions, here demonstrated with CO$_{2}$ methanation using nickel-based catalysts. A series of five Ni/ZrO$_{2}$ catalysts is studied which differ by calcination temperature of the ZrO$_{2}$ support prior to Ni deposition, leading to different textural properties of the support. Artificial thermal aging of the Ni/ZrO$_{2}$ series is then performed and monitored by operando synchrotron-based powder X-ray diffraction (SPXRD). This reveals the dependence of catalyst stability on the support properties and shows that different deactivation mechanisms take place. Catalyst deactivation is mainly correlated either to changes of the support or to changes in nickel crystallite size, depending on the calcination temperature of the support before nickel deposition. By preparing a targeted series of supports with different textural properties, it is possible to deconvolute these effects. Operando SPXRD is shown as a powerful tool to follow both textural and structural changes during thermal catalyst deactivation, which is mostly only performed by post mortem ex situ analysis.