Direct synthesis of CH3OH from CO2 hydrogenation over Ni5Ga3/SiO2 catalysts

Relationship between Structural Properties of the Unsupported Ni5Ga3 Catalyst and Methanol Synthesis Activity

“…Conversely, the diffraction peaks of metallic Ni disappeared completely from the XRD patterns of the as-prepared Ni 5 Ga 3 -500 and Ni 5 Ga 3 -600 catalysts with the new peaks at 2θ = 43.5°and 50.5°emerged (the solid black lines in Figure 1b,c), corresponding to the Ni 5 Ga 3 and Ni 3 Ga alloys, 16 respectively. Reduction at 700 °C encouraged the deep reduction of Ga 2 O 3 into metallic Ga and the formation of Ni 5 Ga 3 alloy (2θ = 43.4°and 48.5°), 32 as evidenced by the emerging of the strong diffraction peak at 2θ = 45°in the XRD pattern of the as-prepared Ni 5 Ga 3 -700 (the solid black bine in Figure 1d), with the disappearance of diffraction peaks of Ga 2 O 3 at 2θ = 36°and 38°(JCPDS 06−0529). However, it is worth noting that metallic Ga species could still exist in the catalysts due to the formation of Ni 3 Ga (which has very low content, being lower than the upper detection limit of XRD), as evidenced by the incomplete reduction of metal phases (supported by the H 2 -TPR results, Figure S2).…”

“…The DRIFT spectra collected under TPSR condition (Figure with the raw data shown in Figure S14) show the presence of characteristic bands of key intermediates including carboxylate (1,623 cm –1 ), formate (1,356 and 1,568 cm –1 ), CO linearly adsorbed on metallic Ni sites (2,055 and 2,077 cm –1 ), and methoxy (1,456 cm –1 ) on different catalysts at different reaction temperatures. ,, Comparatively, the intensity of these bands in Ni 5 Ga 3 -400 is very strong but drops noticeably upon increasing the thermal reduction temperature. In detail, the DRIFT spectra of Ni 5 Ga 3 -400 show significantly strong intensity of IR bands at 1,356, 1,568, and 1,623 cm –1 (Figure a), which are related to the symmetric/asymmetric OCO stretching of monodentate carbonate, carboxylate, and formate adsorbed on Ga 2 O 3 species. ,,, The presence of these species could prohibit the further interaction between CO 2 and Ga 2 O 3 (i.e., poisoning by intermediates) and the H 2 dissociation and spillover, resulting in the lower CO 2 conversion, as evidenced by the activity data (Figure S4a). In addition, the strong adsorption of the intermediates on the active sites might lead to deep hydrogenation as well, being responsible for methane formation (Figure S4c).…”

“…In detail, the DRIFT spectra of Ni 5 Ga 3 -400 show significantly strong intensity of IR bands at 1,356, 1,568, and 1,623 cm −1 (Figure 5a), which are related to the symmetric/asymmetric OCO stretching of monodentate carbonate, carboxylate, and formate adsorbed on Ga 2 O 3 species. 17,19,31,32 The presence of these species could prohibit the further interaction between CO 2 and Ga 2 O 3 (i.e., poisoning by intermediates) and the H 2 dissociation and spillover, 31 resulting in the lower CO 2 conversion, as evidenced by the activity data (Figure S4a). In addition, the strong adsorption of the intermediates on the active sites might lead to deep hydrogenation as well, being responsible for methane formation (Figure S4c).…”

Magnetron Sputtering of Pure δ-Ni5Ga3 Thin Films for CO2 Hydrogenation

“…From the Arrhenius plot of Figure 3c, the catalyst shows an apparent activation energy of around 53 kJ/mol, which is comparable to the commercial CuZn catalyst but slightly higher compared to the one reported in other studies on the same catalyst. 14 It is important to highlight that the comparison of these numbers is mostly reliable when the samples are tested under the exact same conditions. Nevertheless, this serves as a further indication of the remarkable performances and differences of these sputterdeposited δ-Ni 5 Ga 3 thin films for CO 2 hydrogenation to methanol.…”