Catalytic performance and SO2 resistance of zirconia-supported platinum-palladium bimetallic nanoparticles for methane combustion

Abstract

Methane can induce a serious greenhouse effect, and it is highly required to control its emissions. In this work, we used PdCl2 and H2PtCl6 as noble metal precursors, polyvinyl alcohol as protecting agent, and NaBH4 as reducing agent to synthesize the PtPdx bimetallic nanoparticles (NPs), which were then supported on the surface of zirconia to generate the yPtPdx/ZrO2 (i.e., 0.44PtPd2.20/ZrO2, 0.54PtPd0.90/ZrO2, and 0.61PtPd0.48/ZrO2; x and y are the Pd/Pt molar ratio and PtPdx loading, respectively; x = 0.48–2.20; and y = 0.44–0.61 wt%) catalysts. For comparison purposes, we also prepared the 0.55 wt% Pd/ZrO2 (0.55 Pd/ZrO2) and 0.65 wt% Pt/ZrO2 (0.65Pt/ZrO2) catalysts. It was shown that the PtPdx NPs with an average size of 2.4–3.6 nm were highly dispersed on the ZrO2 support. Among these samples, 0.44PtPd2.20/ZrO2 exhibited the best catalytic activity (T50% = 345 °C and T90% = 408 °C at space velocity = 20,000 mL/(g h); apparent activation energy = 59 kJ/mol; turnover frequency (TOFPd) at 350 °C = 124.1 × 10–3 s−1, and specific reaction rate at 350 °C = 466.6 μmol/(gPd s)). The good performance of 0.44PtPd2.20/ZrO2 was associated with its well dispersed PtPd2.20 NPs, high adsorbed oxygen species concentration, good redox ability, large methane adsorption capacity, and strong interaction between PtPdx and ZrO2. Furthermore, the 0.44PtPd2.20/ZrO2 catalyst also possessed excellent thermal stability and good water- and sulfur dioxide-resistant performance. According to the characterization results, we deduce that SO2 could be preferentially adsorbed at the Pt site in 0.44PtPd2.20/ZrO2 and protected the active phase of PdO from being poisoned by SO2, thus improving its SO2 resistance.