Modification of Cu/SiO₂ Catalysts by La₂O₃ to Quantitatively Tune Cu⁺‐Cu⁰ Dual Sites with Improved Catalytic Activities and Stabilities for Dimethyl Ether Steam Reforming

Abstract

Dimethyl ether steam reforming (DME SR) is a promising route to provide H2 for on‐board H2‐based fuel cells. Herein, we synthesized the La2O3‐modified Cu/SiO2 catalyst with dual copper species of Cu0 and Cu+ for DME SR, which exhibits both the high catalytic performance and long‐term stability. The strong electron donor‐acceptor interaction between the lanthanum and copper species occurs after reduction of the catalysts, which is an essential factor to quantitatively determine the ratio of Cu+/(Cu0+Cu+). The addition of La can improve the dispersion of both metallic Cu and Cu2O on the catalysts, as well. After modulating the ratio of Cu+/(Cu0+Cu+) to ∼0.5 by varying the La loading, we achieved the highest activity and lowest CO selectivity. After the durability tests, the results of TEM, EXAFS, and XPS reveal that the addition of La on the Cu/SiO2 catalysts not only stabilizes the copper species from aggregation, especially for the metallic Cu, but also avoids over‐reduction of the Cu+ species to Cu0. The constant ratio of Cu+/(Cu0+Cu+) on the La‐modified Cu/SiO2 catalyst ensures the high catalytic stability in DME SR.

Highly active Ce, Y, La-modified Cu/SiO2 catalysts for hydrogenation of methyl acetate to ethanol

“…The strong interaction between Cu and La might be derived from their close proximity, which would retard the transformation of Cu 2+ to Cu 0 to some extent. 36…”

“…With the increase in La content, the La 3d 5/2 binding energy decreases from 842.8 eV to 841.5 eV due to the increase in electron density of the LaO x species on the surface of the catalyst. 36 Cu LMM Auger electron spectra (XAES) was used to discriminate Cu + and Cu 0 species because these two species are almost located at the same position of binding energy. As shown in Fig.…”

“…As reported previously, the production of more Cu + species may be due to electronic interaction between the copper species and the promoter. 36 This effect would retard the degree of reduction of Cu 2+ species and generate more Cu + on the catalyst surface. Compared to Ce and Y, the La-doped Cu/SiO 2 catalyst exhibits a higher ratio of Cu + /(Cu + + Cu 0 ), indicating that La is more favorable for increasing the surface concentration of Cu + species.…”

Insight into the Correlation between Cu Species Evolution and Ethanol Selectivity in the Direct Ethanol Synthesis from CO Hydrogenation

“…Copper surface area of the catalyst in different stages during reaction was determined by N 2 O titration at 50 °C using the procedure described by H. Xi et al . and Z. Yuan et al . In order to obtain the copper surface area (S Cu(0) ) under reaction temperature (300 °C), the used catalyst was pretreated by 5 % oxygen at 300 °C for 30 min and cooled to 30 °C, which totally oxidized the metallic Cu.…”

“…In heterogeneous catalysis, metals or metal oxides are traditionally dispersed as nanoscale particles on a support with a large surface to maximize the number of exposed active sites . As reported, copper species are much easier to be highly dispersed on Al 2 O 3 or SiO 2 support with large surface in comparison to the TiO 2 support with a small surface. Despite that Al 2 O 3 support has been used for widespread applications, the relatively high quantity of acid sites on Al 2 O 3 surface may catalyze unwanted isomerization or oligomerization reactions according to many studies ,,,.…”