Mechanistic Insights into Selective CO₂ Conversion via RWGS on Transition Metal Phosphides: A DFT Study

Abstract

Selective conversion of CO 2 to CO via the reverse water gas shift (RWGS) reaction is an attractive CO 2 conversion process, which may be integrated with many industrial catalytic processes such as Fischer−Tropsch synthesis to generate added value products. The development of active and cost friendly catalysts is of paramount importance. Among the available catalyst materials, transition metal phosphides (TMPs) such as MoP and Ni 2 P have remained unexplored in the context of the RWGS reaction. In the present work, we have employed density functional theory (DFT) to first investigate the stability and geometries of selected RWGS intermediates on the MoP (0001) surface, in comparison to the Ni 2 P (0001) surface. Higher adsorption energies and Bader charges are observed on MoP (0001), indicating better stability of intermediates on the MoP (0001) surface. Furthermore, mechanistic investigation using potential energy surface (PES) profiles showcased that both MoP and Ni 2 P were active toward RWGS reaction with the direct path (CO 2 * → CO* + O*) favorable on MoP (0001), whereas the COOH-mediated path (CO 2 * + H* → COOH*) favors Ni 2 P (0001) for product (CO and H 2 O) gas generation. Additionally, PES profiles of initial steps to CO activation revealed that direct CO decomposition to C* and O* is favored only on MoP (0001), while H-assisted CO activation is more favorable on Ni 2 P (0001) but could also occur on MoP (0001). Furthermore, our DFT calculations also ascertained the possibility of methane formation on Ni 2 P (0001) during the RWGS process, while MoP (0001) remained more selective toward CO generation.

Microwave one-pot synthesis of CNT-supported amorphous Ni–P alloy nanoparticles with enhanced hydrogenation performance

“…Transition metal phosphides have shown outstanding catalytic performance in many applications including hydrogen evolution reaction (HER), 37 oxygen evolution reaction (OER), 38 CO 2 conversion, 39,40 and hydrogenation reactions. 28 In particular, amorphous Ni-P alloy catalysts have high activity in a wide range of hydrogenation reactions, probably due to the highly unsaturated metal active sites in the amorphous structure and the electronic interaction between Ni and P. 7 In this work, the selective hydrogenation of nitroarenes to primary amines was used as the probe reaction to study the catalytic performance of Ni-P/CNTs-MA.…”

Dynamic Microkinetic Modeling for Heterogeneously Catalyzed Hydrogenation Reactions: a Coverage-Oriented View

“…In all the previous models, all reactions are carried out over a single type of site. However, in industrial production, complex catalysts are usually applied; − thus, various sites can participate in the reaction process. Even when a simple catalyst is applied, it still involves various sites composed of different facets, edges, or even defects. , …”

“…A number of practical reactions of interest, such as reversed water–gas shift , and methanol synthesis, , include at least one surface decomposition reaction step, which leads to a side product. This introduces more coupling correlations in the microkinetic model, which should be addressed to expand the generality of the method.…”

The Role of Hydrogen Adsorption Site Diversity in Catalysis on Transition Metal Phosphide Surfaces

“…37 Even on the same facet (i.e., Ni2P(0001)), there are multiple possible surface terminations (e.g., Ni3P2 and Ni3P terminations). 37,38 In Figure 2 we summarize the computed HBE on Ni2P(0001) and CoP (101) surfaces from reported values in the literature. The calculated HBE at the Ni3 hollow site on the Ni2P(0001) surface ranges from 0.137 to -0.543 eV.…”

“…DFT studies delve further into the energetics of the TMP-catalyzed reverse water-gasshift (RWGS) reaction, which suggest that the ability to dissociate H2 on Ni2P and MoP is a source of their ability to catalyze RWGS. 101 Similar to HDS, we believe it is necessary to extend this idea to other adsorbates. Cui et al used temperature programmed reduction and oxidation to measure the affinity of H2 and CO2 for catalyst surfaces.…”