(187k) Bimetallic Pd-Cu Catalysts for CO2 Hydrogenation to Methanol | AIChE

(187k) Bimetallic Pd-Cu Catalysts for CO2 Hydrogenation to Methanol


Jiang, X. - Presenter, Georgia Institute of Technology
Nie, X., Dalian University of Technology
Guo, X., Dalian University of Technology
Walton, K., Georgia Institute of Technology
Song, C., Pennsylvania State University
Bimetallic Pd-Cu Catalysts for CO2 Hydrogenation to Methanol

Xiao Jiang1,2, Xiaowa Nie2,3, Xinwen Guo2,3, Krista Walton1, Chunshan Song2,3*

1 School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., GA 30332, USA

2 Clean Fuels & Catalysis Program, PSU-DUT Joint Center for Energy Research, EMS Energy Institute, The Pennsylvania State University, 209 Academic Projects Building, PA 16802, USA

3 PSU-DUT Joint Center for Energy Research, School of Chemical Engineering,

Dalian University of Technology, Dalian 116024, China

Email: csong@psu.edu

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 andseeks to clarify if the combination of Pd and Cu could synergetically promote CH3OH formation from CO2/H2 and to develop a fundamental understanding on the composition-structure-alloy-catalytic property relationship.

A strong synergetic effect on promoting methanol formation was observed over Pd-Cu bimetallic catalysts supported on amorphous silica 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 the corresponding monometallic catalysts. To examine the origin of the synergetic promotion, the reduced catalysts were characterized by TPR, XRD, TEM, STEM/EDS, and H2-/CO2-TPD. The results demonstrated that the 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. The correlation of alloys with the activity performance indicates 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.

The catalytic performance was also studied at lower metal loading but maintaining the optimal bimetallic composition. Not only did the metal efficiency-based CH3OH yield well retained when decreasing the metal loading from 18.7 to 2.4 wt%, but it also exhibited almost 2-fold more CH3OH than the commercial Cu-ZnO-Al2O3 catalyst. Albeit such advantage, the Pd-Cu catalysts with lower metal loading yielded more CO, which is attributed to the Cu-rich alloy surface. Evidently, the product distribution strongly depends on the alloy composition.

The alloy composition-dependent behavior was investigated by both computational and experimental work, wherein PdCu alloy composition is superior for both CO2 and H2 activation and subsequent hydrogenation to CH3OH in comparison to PdCu3 alloy composition.

These findings would be of critical importance for developing new catalysts and catalytic CO2 hydrogenation process technology and for fundamental understanding of chemistries involving in CO2 hydrogenation to CH3OH