Evolution of Cu-Zn-Si oxide catalysts in the course of reduction and reoxidation as studied by in situ X-ray diffraction analysis, transmission electron microscopy, and magnetic susceptibility methods

Dynamic Cu/Zn Interaction in SiO2Supported Methanol Synthesis Catalysts Unraveled by in Situ XAFS

“…Similarly, under nonhydrothermal conditions the formation of a copper–zinc hydrosilicate phase of the zincsilite-type was demonstrated in the Cu/ZnO/SiO 2 (CZS) system by Yurieva et al , using XRD, HRTEM, and IR. The occurrence of this phase was further confirmed in a more recent investigation of the CZS system that pointed out a linear increase of the activity in the methanol synthesis with the Zn content, indicating the active site may also be closely related to the Zn phase …”

“…More recently the formation of a CuÀZn α-brass with 24% Zn was clearly evidenced by XRD on a similar CuÀZnÀSiO 2 system with a lower Cu/Zn ratio of 0.41 (Cu 18.6 wt % and Zn 44.8 wt %), prepared with the same method and reduced above 600 °C. 18 This indicates that, as the reduction temperature increases, the Cu/Zn hydrosilicate phase in CZS is progressively transformed into (i) Cu 0 , (ii) increasingly dispersed ZnO species on SiO 2 , and (iii) finally into a Zn metallic phase forming CuÀZn α-brass alloy particles. This is in line with LEIS results showing that dispersed ZnO is covering the Cu particles but also the SiO 2 support with a significantly more pronounced effect in CZS-R400 than in CZS-R300.…”

“…13 This general interpretation is in line with the more recent results obtained on a similar CuÀZnÀSiO 2 catalysts with a different Cu/Zn ratio that demonstrated a sharp increase of the activity in the methanol synthesis as a function of the Zn content as well as the reduction temperature employed. 18 On a comparable Cu/Zn/SiO 2 catalyst (39 wt % Cu, 13 wt % Zn, Cu/Zn = 3), the activity k varied from 7.8 Â 10 À5 for the material reduced at 220°C to 2.3 Â 10 À4 reduced at 250°C. Similarly, when the Zn content increased to 44.8 wt % the k value increases sharply to 3.07 Â 10 À4 when reduced at 220°C up to 1 Â 10 À3 for the material reduced at 250°C.…”

Hydrogenation of lactic acid on reduced copper-containing catalysts

“…It is important that the copper particles are stable and do not suffer sin tering in a wide temperature interval. 17, 19 In the present work, we attempted to compare the properties of the catalysts in the hydrogenation of lactic acid.…”

“…[13][14][15][16][17][18][19] To activate catalyst precursors, a weighed sample of the precursor (0.5 g) was placed in a fixed bed reactor and treated with hydrogen with a flow rate of 4-10 L h -1 at 653 K.…”