The role of PdZn surface alloy composition, PdZn particle size, and ZnO structure in steam reforming of alcohols
EMSL Project ID
34906
Abstract
Pd/ZnO has been shown in recent years to possess high selectivity towards CO2 during methanolsteam reforming. It was first proposed that PdZn alloy formation is essential to achieve high selectivity towards CO2. While PdZn can be formed readily by pretreating Pd/ZnO in H2 at 250°C, higher pretreatment temperatures have been seen to increase conversion even while the surface area of the metallic phase decreases. Previous work has also shown that selectivity to CO2 is in fact reduced for PdZn particle diameters less than ~10 nm. The goal of this work is to understand the role of PdZn as well as the role of the ZnO support on catalyst activity and selectivity for alcohol steam reforming. We would like to combine computational and experimental approaches to improve our understanding of the importance of PdZn alloy particles and ZnO supports using the EMSL facilities.
1. The first objective is to use state-of-the-art computational strategies based on density-functional-theory (DFT) to investigate the role of PdZn and ZnO on alcohol reforming. For PdZn we will investigate different low (Miller) index surfaces to determine the relative stability of these surfaces and the effect of surface chemistry on surface relaxation, electronic work function and the electronic density of states. The PdZn investigation will include the role of PdZn particle size and Pd to Zn ratio on the density of states. For ZnO, the effects of surface vacancies on the electronic structure of the <0001> and <10-10> surfaces as well as the role of different surface structures will be investigated. The energies of adsorption of known intermediates in the alcohol reforming reaction including CO, CO2, CH2O, and CH3CHO will then be calculated for the most stable PdZn and ZnO surfaces.
2. The second objective is to utilize the PNNL experimental facilities to study bulk PdZn alloy powders of various compositions and ZnO-supported PdZn to investigate the effects of PdZn composition, PdZn particle size, ZnO surface area, and ZnO surface structure.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2009-10-05
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Halevi B, EJ Peterson, A Roy, A DelaRiva, E Jeroro, F Gao, wang, JM Vohs, B Kiefer, EL Kunkes, M Havecker , M Behrens, R Schlogl, and AK Datye. 2012. "Catalytic Reactivity of Face Centered Cubic PdZna for the Steam Reforming of Methanol." Journal of Catalysis 291:44-54. doi:10.1016/j.jcat.2012.04.002
Lebarbier VMC, Y Wang, AK Datye, B Halevi, JM Vohs, E Jeroro, B Kiefer, EL Kunkes, R Schlogl, E Peterson, A DelaRiva, M Havecker , and M Behrens. 2010. "Aerosol-Derived Bimetallic Alloy Powders: Bridging the Gap." PNNL-SA-76995, Pacific Northwest National Laboratory, Richland, WA.
Peterson EJ, B Halevi, B Kiefer, MN Spilde, AK Datye, J Peterson, LL Daemen, A Llobet, and H Nakotte. 2011. "Aerosol synthesis and Rietveld analysis of tetragonal (??) PdZn." Journal of Alloys and Compounds 509(5):1463-1470. doi:10.1016/j.jallcom.2010.09.149
The effect of PdZn particle size on reverse-water?gas-shift reaction, Applied Catalysis A: General 379 3?6 2010, Lebarbier, V. Dagle, R. Datye, A.K., Wang, Y.