Periodic Trends from Metal Substitution in Bimetallic Mo-Based Phosphides for Hydrodeoxygenation and Hydrogenation Reactions

Abstract

Bimetallic phosphides are promising materials for biomass valorization, yet many metal combinations are understudied as catalysts and require further analysis to realize their superior properties. Herein, we provide the synthesis, characterization, and catalytic performance of a variety of period 4 and 5 solid solutions of molybdenum-based bimetallic phosphides (MMoP, M = Fe, Co, Ni, Ru). From the results, the charge sharing between the metals and phosphorus control the relative oxidation of Mo and reduction of P in the lattice, which were both indirectly observed in binding energy shifts in X-ray photoelectron spectroscopy (XPS) and absorption energy shifts in X-ray absorption near-edge spectroscopy (XANES). For MMoP (M = Fe, Co, Ni), the more oxidized the Mo in the bimetallic phosphide, the higher the selectivity to benzene from phenol via direct deoxygenation at 400 °C and 750 psig. This phenomenon was observed in the bimetallic materials synthesized across period 4, where aromatic selectivity and degree of Mo oxidation both decreased in the following order FeMoP ≫ CoMoP > NiMoP. Alternatively, in the case of MMoP (M = Fe, Ru), the P in RuMoP is more oxidized compared to that in FeMoP, and the selectivity toward the hydrogenation pathway increased due to the interaction between the aromatic rings and the P species on the surface. For RuMoP and NiMoP, cyclohexanol was selectively produced from phenol with >99% selectivity when the reaction temperature was lowered to 125 °C at 750 psig, whereas FeMoP and CoMoP were not active under these conditions. Last, complete deoxygenation of phenol to benzene, cyclohexane, and cyclohexene was accomplished using mixtures of RuMoP and FeMoP in flow and batch experiments. These results highlight the versatility and wide applicability of transition metal phosphides for biomass conversions.

Catalytic Hydrogen Transfer and Decarbonylation of Aromatic Aldehydes on Ru and Ru Phosphide Model Catalysts

“…Overall, the presence of P atoms alters the catalytic properties of Ru(0001) likely as a consequence of charge transfer from Ru to P atoms on the surface, which reduces the extent of electron exchange between metal atoms and the adsorbates. 71 These resulting changes in the product distribution show that these differences in the electronic structure of Ru apparently increase barriers and reduce reactivity for C−O, C−C, and C−H bond ruptures. However, these results cannot exclude the possibility that changes in the Ru−Ru coordination and bond lengths caused by the presence of P atoms modify surface chemistry by ensemble effects.…”

The Effects of P-Atoms on the Selective Dehydrogenation of C6H10 over Model Ru Surfaces

“…Moreover, TPR of C 6 H 6 also suggests that P atoms significantly decrease the C 6 H 6 binding energy and extent of C 6 H 6 decomposition in comparison to Ru(0001), which can promote C 6 H 6 desorption over decomposition and lead to decreased coking during TPR of C 6 H 10 (Figure S3). While these results indicate that the presence of P atoms within the P 0.4 -Ru­(0001) surface withdraw charge from Ru atoms, consistent with XPS of related TMP nanoparticles, − Muetterties et al demonstrated that adsorption of trimethyl phosphine could liberate reactive intermediates of dehydrogenation reactions from Ni , and Pt surfaces. To further understand the dehydrogenation selectivity and intrinsic barriers, we probe the mechanism of C 6 H 10 dehydrogenation over Ru(0001) and P 0.4 -Ru­(0001).…”

“…Previously reported Bader charge analysis and differences among core-electron binding energies detected by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure demonstrate that charge transfers from transition metals to P in TMP, which results in electronic modifications of the transitions metals. − These electronic modifications decrease the binding energy of the dehydrogenation product and facilitate the desorption of olefins over further dehydrogenation. In addition, these electronic changes − can modify the binding modes and configuration of surface intermediates caused by interactions with cationic metal and anionic P atoms exposed at surfaces. ,, …”

Ethane dehydrogenation performance and high temperature stability of silica supported cobalt phosphide nanoparticles

“…P-Containing catalysts, also known as metal phosphides, are known particularly for hydrodesulfurization, hydrodeoxygenation, and hydrogenation reactions. [8][9][10][11][12][13] Additionally, many metal phosphides are made from earth abundant metals, such as Ni, Co, Mo, and Fe, and have been identified as promising alternatives to noble metal based catalysts for many industrially relevant reactions. 14,15 For light alkane dehydrogenation reactions, P promotion of Ni results in improved selectivity to the desired alkene as well as improved stability over monometallic Ni nanoparticles.…”