Highly active SiO2-supported palladium nanoparticles prepared by a modified ammonia evaporation method for lean methane oxidation

Abstract

By optimizing the ammonia evaporation (AE) method, highly active palladium nanoparticles were successfully deposited on fumed silica (f-SiO2) and exhibited excellent catalytic activity for the catalytic combustion of methane (CCM). It was manifested that the timing of ammonia introduction was of great importance in determining the particle sizes and electronic states of palladium nanoparticles, the desilication degree of SiO2 support material, and the redox properties and methane affinity of the Pd/f-SiO2-AE catalysts. The optimal Pd/f-SiO2-AE-2 catalyst, which converted 90% of lean methane at 333 °C at GHSV of 30,000 h − 1, performed better than its AE-1- and IM-prepared counterparts. In combination with complementary characterizations, DFT calculations and designed experiments, it was revealed that the uniformly dispersed palladium nanoparticles endowed the Pd/f-SiO2-AE-2 catalyst with more accessible sites. Moreover, the presence of Pd4+ species effectively promoted the methane adsorption capacity of the main active PdO phase, which was another critical reason for the outstanding performance. In addition, the necessity of the ammonia evaporation step was also elucidated by designed experiments. More importantly, taking the universality of this optimized AE method into consideration, our work thus put forward an effective and simple procedure to fabricate highly-active palladium nanoparticles for catalyst designers.