The roles of Rh crystal phase and facet in syngas conversion to ethanol

Syngas Conversion to C2 Species over WC and M/WC (M = Cu or Rh) Catalysts: Identifying the Function of Surface Termination and Supported Metal Type

“…The Rh/WC–C catalyst kinetically prefers the reaction of CO + H → CHO (170.1 kJ·mol –1 ) in comparison with CO → C + O and CO + H → COH. However, COH generation (94.7 kJ·mol –1 ) over Rh/WC–W catalyst is preferable kinetically; our previous studies showed that Rh(111) prefers the reaction of CO + H → CHO (139.9 kJ·mol –1 ) rather than the reactions of CO + H → COH and CO → C + O. Thus, compared to the Rh catalyst, the exposed termination of WC support in the Rh/WC catalysts can change the optimal CO activation path, especially the Rh/WC–W catalyst enhances the ability of CO initial activation.…”

“…Thus, compared to the Cu catalyst, the WC support in the Cu/WC–W and Cu/WC–C catalysts alters the optimal path of CH generation. In Figure d,e, over the Rh/WC–C and Rh/WC–W, the process of CO + H → COH + (H) → CHOH → CH + OH is kinetically favored; however, the process of CO + H → CHO + (H) → CHOH → CH + OH is kinetically favored over Rh(111); namely, WC support changes the optimal path of CH generation.…”

“…Furthermore, previous studies showed that the abundant CH x monomer were both CH 2 and CH 3 with the overall barriers of 149.3 and 145.6 kJ•mol −1 over the Cu(111) surface, 3 whereas CH serves as the abundant CH x monomer over Rh(111) surface, which requires the overall barrier of 225.9 kJ•mol −1 . 41 More importantly, compared to the Cu catalyst, the Cu/ WC−C catalyst greatly enhances the activity of the abundant CH x monomer (149.3 and 145.6 vs 28.7 kJ•mol −1 ), while the Cu/WC−W catalyst decreases the activity of the abundant CH x monomer (155.7 vs 149.3 and 145.6 kJ•mol −1 ). Similarly, compared to the Rh catalyst, the Rh/WC−W catalyst increases the activity of the abundant CH x monomer (121.5 vs 225.9 kJ• mol −1 ), whereas the Rh/WC−C catalyst reduces the activity of the abundant CH x monomer (252.6 vs 225.9 kJ•mol −1 ).…”

“…3 Over the Rh/WC−C and Rh/WC−W catalysts, CH 3 and CH 2 serve as the abundant CH x monomer, respectively, whereas CH serves as the abundant CH x monomer over Rh(111). 41 The WC support in the M/WC−C (M = Cu or Rh) catalysts impacts the existence of the abundant CH x monomer in comparison with the Cu and Rh catalysts. Meanwhile, the generation rate (s −1 •site −1 ) of the abundant CH x monomer follows the sequence Cu/WC−C (1.65 × 10 1 ) > Rh/WC−W (2.89 × 10 −3 ) > WC−W (6.32 × 10 −5 ) > Rh/WC−C (4.00 × 10 −11 ) > Cu/WC−W (2.04 × 10 −16 ); namely, Cu/WC−C presents the highest activity toward abundant CH x monomer.…”

“…For the Cu/WC and Rh/WC catalysts, the C-termination of WC contributes to C 2 species generation, while the W-termination is only preferable for CH 3 OH generation. Thus, starting from CH, CH 2 , and CH 3 , the generation of methane and C 2 species over the WC−W, Cu/WC−C, and Rh/WC−C catalysts are considered to identify the most suitable catalyst toward C 2 However, on Rh(111), 41 the main product is CHCHO rather than methane; thus, the WC support in Rh/WC−C catalyst also changes the type of dominant product.…”