PdZn nanoparticle catalyst formation for ethanol dehydrogenation: Active metal impregnation vs incorporation

摘要

Two hydrotalcite-based catalysts have been prepared to investigate the effect of synthesis methods on the catalyst behavior in ethanol dehydrogenation to acetaldehyde. On the first one, PdZn/Mg(Al)O-x, Pd and Zn were impregnated on the hydrotalcite support while on the second one, PdZn/Mg(Al)(Pd)(Zn)O-x, Pd and Zn were both incorporated during the support synthesis. Extensive catalyst characterization such as EXAFS, XPS, STEM, XRD,... allowed concluding that impregnation of the active metals gives rise to larger nanoparticles compared to incorporation. Impregnation provokes incomplete reduction, yielding nanoparticles with a PdZn shell and a Pd core. More homogeneously alloyed nanoparticles were obtained after incorporation. The higher methane selectivity on the impregnated catalyst is in agreement with the less uniformly alloyed nanoparticles, which more likely exhibit adjacent Pd-sites promoting product acetaldehyde decomposition. Overall, incorporation gave rise to the most active and selective catalyst to acetaldehyde for ethanol dehydrogenation to acetaldehyde.