In Situ-DRIFTS Study of Rh Promoted CuCo/Al₂O₃for Ethanol Synthesis via CO Hydrogenation

Abstract

The promoting effect of rhodium on the structure and activity of the supported Cu-Co based catalysts for CO hydrogenation was investigated in detail. The samples were characterized by DRIFTS, N 2 -adsorption, XRD, H 2 -TPR, H 2 -TPD and XPS. The results indicated that the introduction of rhodium to Cu-Co catalysts resulted in modification of metal dispersion, reducibility and crystal structure. DRIFTS results of CO hydrogenation at reaction condition (P=2 MPa, T=260 o C) indicated the addition of 1 wt % rhodium improved hydrogenation ability of Cu-Co catalysts. The ethanol selectivity and CO conversion were both improved by 1 wt % Rh promoted Cu-Co based catalysts. The alcohol distribution over un-promoted and rhodium promoted Cu-Co based catalysts obeys A-S-F rule and higher chain growth probability was got on rhodium promoted catalyst.

Mechanistic Aspects of the Role of K Promotion on Cu–Fe-Based Catalysts for Higher Alcohol Synthesis from CO2 Hydrogenation

“…On further increasing the temperature to 250 °C, *HCOO (2937/2866/1620/1393 cm –1 ) almost disappears and gaseous CO (2179/2110 cm –1 ) and bri-CO are greatly increased (Figure S10e,f), suggesting the transformation of *HCOO to CO. , However, the peak of lin-CO is very weak and covered by gaseous CO peak, which further proves that bri-CO is more favorable than lin-CO over 0.1K-CMZF. In the meantime, gaseous CH 4 (3016 cm –1 ) and adsorbed *CH x species (2900–3000 cm –1 ) appear (Figure a). , As the reaction temperature increases to 300 °C, the peak of gaseous CO is retained and that of *CH 3 O vanishes (Figure S10g,h) because RWGS is endothermic while methanol synthesis (MS) is exothermic. The peak of bri-CO shifts to 1917 cm –1 (Figure S10h), suggesting that the CO π bond is further weakened.…”

“…In the meantime, gaseous CH 4 (3016 cm −1 ) and adsorbed *CH x species (2900− 3000 cm −1 ) appear (Figure 3a). 57,58 As the reaction temperature increases to 300 °C, the peak of gaseous CO is retained and that of *CH 3 O vanishes (Figure S10g,h) because RWGS is endothermic while methanol synthesis (MS) is exothermic.…”

Active Centers of Catalysts for Higher Alcohol Synthesis from Syngas: A Review

“…On the other hand, additional elements such as Mn, − Rh, Nb, Zr, Cr, , and La in the Co–Cu-based catalysts could act as structural promoters or synergetic promoters, which also improved the HA yield.…”

“…With only 1 wt % Rh addition, the trimetallic Co−Cu−Rh/ Al 2 O 3 catalyst exhibited better performance for HAS than the Co−Cu bimetallic catalyst (CO conversion 36.7% vs 26.7% and C 2+ OH selectivity 24.3% vs 10%, respectively). 289 The promotion of Rh is reflected not only in the hydrogenation ability but also the surface concentration of Cu, which could provide more active sites for CO insertion.…”

Sulfate-Promoted Higher Alcohol Synthesis from CO2 Hydrogenation

“…In situ diffuse reflectance infrared Fourier transformation spectroscopy (in situ DRIFTS) experiments were conducted to investigate the reaction intermediates on the surface of the 0.6S-KCFZ catalyst. As seen in Figure , there emerge HCOO* (1357, 1525, 1612, 2897, and 2976 cm –1 ), C 2 H 5 O* (1067, 2911, and 2962 cm –1 ), CH 3 CHO* (2764 cm –1 ), and CO (2110, 2171 cm –1 ) species as the CO 2 hydrogenation reaction progressed. ,− The formation of higher alcohols involves a tandem process of the RWGS reaction, CO dissociated to CH x species, CO insertion, and hydrogenation of CH 3 CHO*. , The successful observation of these intermediates proves the CO-mediated reaction pathway in HAS.…”