Composition Tuning of Ru-Based Phosphide for Enhanced Propane Selective Dehydrogenation

Abstract

In this work, we report a robust Ru phosphide (RuP) catalyst, which exhibits high propylene selectivity for propane dehydrogenation, whereas monometallic Ru nanoparticles (NPs) result in cracking. X-ray photoelectron spectroscopy, synchrotron X-ray absorption spectroscopy, transmission CO-IR of the reduced catalyst, and high-angle annular dark-field scanning transmission electron microscopy are used to identify the surface structure of NPs with different P/Ru atomic ratios, changing from Ru to Ru2P to RuP with increasing P loading. In addition to improving the olefin selectivity, increasing the P/Ru ratio leads to higher turnover rates and lowers the deactivation rate. P is thought to act as a structural promoter to reduce the Ru ensemble size, decreasing the hydrogenolysis rate. In addition, increasing the P/Ru ratio leads to a decrease in the energy of the Ru valence orbitals, which are suggested to weaken metal-adsorbate bond energies and reactant surface coverages.

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

“…These results demonstrate that P incorporation significantly enhances the EDH performance of Co, which is consistent with the trends observed for light alkane dehydrogenation with other P promoted metals such as Ni, Ru, and Pt. [16][17][18][19][20]36 Co 2 P-E/SBA-15 was compared to reported catalytic results of EDH in literature and displayed comparable TOF values to Pt based alloys and other materials tested for EDH (Table S2 †). The H 2 to C 2 H 6 ratio for Co 2 P-E/ SBA-15 was also varied from 0 : 1 to 1 : 1 (Fig.…”

“…44,48,50 Additionally, this shift to higher wavenumbers for room temperature CO adsorption IR studies has been seen in other metal phosphides which have partially positively charged metal sites. 12,20,51 There were no noticeable trends in the 2060 cm −1 peak with P content. This is not surprising due to the complex nature of the catalyst surface with varying P : Co ratio as both the phase as well as the amount of excess P on the surface varies (Fig.…”

“…Specifically, geometric isolation of the metal active sites through the presence of P in the crystal structure helps to limit structure sensitive side reactions, such as hydrogenolysis. 16,17,20,21 Electronic effects from P incorporation lead to a partial positive charge on Ni. This positive charge has been shown to weaken hydrocarbon-metal bonds, resulting in improved selectivity.…”

“…This positive charge has been shown to weaken hydrocarbon-metal bonds, resulting in improved selectivity. 16,17,20,21 In our previous work, we synthesized and evaluated Ni 2 P for ethane dehydrogenation (EDH) and found that P not only promotes the active metal site but also participates in the reaction pathway. In particular, density functional theory calculations predicted the pathway for deep dehydrogenation of ethylene involves the migration of surface bound ethylene to a Ni-P bridge site, resulting in a higher barrier for deep dehydrogenation of ethylene on Ni 2 P and suggesting ethylene desorption as the preferred pathway.…”

Modeling phase formation on catalyst surfaces: Coke formation and suppression in hydrocarbon environments

“…Coke formation on catalyst surfaces is a major cause of catalyst deactivation in several industrial reactions involving hydrocarbon-rich environments, such as Fischer-Tropsch synthesis, [33][34][35][36] methane reforming, [37][38][39][40] CO 2 reduction, 41 fluid catalytic cracking, 42,43 and hydrocarbon dehydrogenation. 44,45 Various strategies have been developed to suppress coke formation, typically by adding promoters and dopants, [46][47][48] forming metal phosphides or sulfides, [49][50][51][52] forming nitrides or carbides, 44,53 or alloying with less carbophilic metals. [54][55][56] The particular interest in this work is the suppression of coke formation during nonoxidative propane dehydrogenation (PDH).…”