Utilization of CO2 as a carbon source for synthesizing chemical feedstocks and transportation fuels has recently attracted great attention worldwide. The present work involves Pd-Cu bimetallic catalysts for CO2 hydrogenation to CH3OH and seeks to clarify if the combination of Pd and Cu could synergetically promote CH3OH formation from CO2/H2 and the relationship of catalyst composition-structure-activity. A strong synergetic effect on promoting methanol formation was observed over amorphous silica-supported Pd-Cu bimetallic catalysts when the Pd/(Pd+Cu) atomic ratios lied within 0.25-0.34 mol mol-1. The optimal CH3OH STY and selectivity were obtained on Pd(0.34)-Cu/SiO2 (e.g., 0.31 μmol g-1 s-1 and 34 mol%, respectively), which was almost 3 times as much as the simple summation of those over monometallic catalysts. To clarify the composition-structure-activity relationship of Pd-Cu bimetallic catalysts, the reduced catalysts were characterized by TPR, XRD, TEM, STEM/EDS, and H2-/CO2-TPD. Detailed characterization results demonstrated that the change of metallic phases varied with the Pd/(Pd+Cu) atomic ratios, and uniform alloy phases PdCu3 and PdCu, were found at Pd/(Pd+Cu) atomic ratio of 0.34 with an average crystallite size around 5 nm. TPD results indicated that the combination of Pd and Cu significantly promoted the adsorption towards weakly-bonded H2 and CO2 on the catalyst surface, the amount of which appear to correlate with the improved CH3OH formation rate. Therefore, the correlation of alloys with the activity performance indicated that the coexistence of nano-sized and uniform Pd-Cu alloy particles, PdCu3 and PdCu, played a crucial role in the observed bimetallic CH3OH promotion. Conversion-selectivity profile suggested that CO2 was a primary carbon source for methanol synthesis at lower CO2 conversion, and byproduct CO contributed at relatively higher CO2 conversion within the conversion range examined.

Bimetallic Pd-Cu catalysts for CO2 hydrogenation to methanol

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.