The New Direction grant is aimed at the elucidation of the mechanism of methanol steam reforming (MSR) using the plane-wave density functional theory (DFT). In the previous funding year, much progress has been made.
We have reported1 an extensive investigation of MSR on Cu(111), and identified a key reaction step that is responsible for the selectivity towards CO2. This reaction between adsorbed formaldehyde (CH2O*) and hydroxyl (OH*), generated from decomposition of methanol (CH3OH*) and water (H2O*), has a small barrier and large exothermicity. The small barrier allows the reaction to compete effectively with the desorption of formaldehyde as well as its further dehydrogenation. The product of the reaction, namely CH2OOH, is shown to produce several intermediates, including formate (CHOO*), formic acid (CHOOH*), and dioxomethylene (CH2OO**), which all lead to CO2. This mechanism is consistent with all experimental data, and in good agreement with other theoretical studies. This paper has been published on Phys. Chem. Chem. Phys.
We have further explored2 an alternative mechanism on the copper catalyst, which involves the surface methyl formate (CHOOCH3*) species. Our results indicated that the methyl formate is indeed a reaction intermediate in MSR, but is unlikely to be the major pathway. Our results helped to explain several pieces of experimental observations related to the formation and reaction of methyl formate on Cu. This paper is being published on the newly established ACS journal, ACS Catalysis.
Furthermore, we have compared several key MSR reaction steps on PdZn and Cu. Our results demonstrated that the reactions are quite similar on the two catalysts.3 In the near future, we will explore other reaction pathways on PdZn, including the methyl formate one studied on Cu already. These studies will provide a complete picture of MSR on two important catalysts.
(1) Lin, S.; Johnson, R. S.; Smith, G. K.; Xie, D.; Guo, H. Phys. Chem. Chem. Phys.2011, 13, 9622.
(2) Lin, S.; Xie, D.; Guo, H. ACS Catal.2011, in press.
(3) Lin, S.; Xie, D.; Guo, H. J. Phys. Chem. C2011, submitted.