Mechanistic Understanding of Alloy Effect and Water Promotion for Pd-Cu Bimetallic Catalysts in CO₂ Hydrogenation to Methanol

Abstract

Density functional theory (DFT) calculations on Pd-Cu bimetallic catalysts reveal that the stepped PdCu(111) surface with coordinatively unsaturated Pd atoms exposed on the top is superior for CO 2 and H 2 activation and for CO 2 hydrogenation to methanol in comparison to the flat Cu-rich PdCu 3 (111) surface. The energetically preferred path for CO 2 to CH 3 OH over PdCu(111) proceeds through CO 2 * → HCOO* → HCOOH* → H 2 COOH* → CH 2 O* → CH 3 O* → CH 3 OH*. CO formation from CO 2 via a reverse water-gas shift (RWGS) proceeds more quickly than CH 3 OH formation in terms of kinetic calculations, in line with experimental observation. A small amount of water, which is produced in situ from both RWGS and CH 3 OH formation, can accelerate CO 2 conversion to methanol by reducing the kinetic barriers for O−H bond formation steps and enhancing the TOF. Water participation in the reaction alters the rate-limiting step according to the degree of rate control (DRC) analysis. In comparison to CO 2 , CO hydrogenation to methanol on PdCu(111) encounters higher barriers and thus is slower in kinetics. Complementary to the DFT results, CO 2 hydrogenation experiments over SiO 2 -supported bimetallic catalysts show that the Pd-Cu(0.50) that is rich in a PdCu alloy phase is more selective to methanol than the PdCu 3 -rich Pd-Cu(0.25). Moreover, advanced CH 3 OH selectivity is also evidenced on Pd-Cu(0.50) at a specific water vapor concentration (0.03 mol %), whereas that of Pd-Cu(0.25) is not comparable. The present work clearly shows that the PdCu alloy surface structure has a major effect on the reaction pathway, and the presence of water can substantially influence the kinetics in CO 2 hydrogenation to methanol.

Metal‐free Catalyst B2S Sheet for Effective CO2 Electrochemical Reduction to CH3OH

“…Although the thermodynamic energy of cis ‐COOH* is similar to that of trans ‐*COOH with only 0.04 eV difference, the activation energy barrier is 0.58 eV for their mutual transformation. Since the activated proton comes from the surface of the catalyst, it is more favorable to form trans ‐*COOH, in which the surface H* directly attacks the O atom of CO 2 as shown in Figure . As one can see, the free energy change of CO 2 hydrogenation to trans ‐*COOH is 0.77 eV, while the decomposition of *COOH to *CO and H 2 O is exothermic with the thermodynamic energy barrier of −0.47 eV.…”

Influences of particle size and crystallinity of highly loaded CuO/ZrO2 on CO2 hydrogenation to methanol

“…Catalytic hydrogenation of CO 2 to methanol is an attractive pathway as it is an important feedstock . So far, various catalysts for this reaction, such as Cu/ZrO 2 , Cu‐Ag/ZrO 2 , Cu/ZrO 2 /SiO 2 , Cu/ZnO/ZrO 2 , Cu/CeO 2 /TiO 2 , MnO x /m‐CoO x , InO 2 /ZrO 2 , Cu‐In/SiO 2 , Ni‐Ga/SiO 2 , ZnO/ZrO 2 , Pd/ZnO, Pd‐Cu/SiO 2 , and Cu/ZnO/Al 2 O 3 , have been proposed. Among them, the Cu/ZrO 2 catalyst would be a promising candidate because of its activity and selectivity for CO 2 hydrogenation to methanol (S. Tada et al, unpublished data) …”

A Mechanism Investigation of how the Alloying Effect Improves the Photocatalytic Nitrate Reduction Activity of Bismuth Oxyhalide Nanosheets

“…[14][15][16][17][18][19] Recently, designing alloyed semiconductors has become an exciting research area for constructing highly active new photocatalysts due to the unique influence of alloying characteristics on the geometry structure and electronic distribution. [20,21] Bismuth-based ternary oxide photocatalysts, bismuth oxyhalides (BiOXs, X=Cl, Br, I), are the typical visible light photocatalyst and have excellent catalytic activity than other materials. [22] Recent studies show that alloying another halogen into bismuth oxyhalides to form the alloyed bismuth oxyhalides (BiOCl n Br 1-n , BiOCl n I 1-n , and BiOBr n I 1-n ) will lead to it possesses much more active than their monohalide counterparts.…”