The Role of the Coprecipitation Sequence of Salt Precursors on the Genesis of Cu-ZnO-Al2O3 Catalysts: Synthesis, Characterization and Activity for Low Temperature Shift Reaction
Abstract:Cu-ZnO-Al2O3 catalysts for the low-temperature water-gas shift reaction were prepared using methods of direct and reverse coprecipitation. The catalysts obtained were characterized by DRX, TPR, XPS, N2O chemisorption, Hg-Porosimetry and BET surface area. It was observed that the precipitation sequence of the precursors led to significant differences in values of copper dispersion and consequently in the activity of the catalyst for the water-gas shift reaction
“…In addition, weak Cu 2p3/2 satellite peak are also observed at around 10 eV higher (B.E. about 940-945 eV) for the CuO/Al2O3, and copper-rich sample (1:4, 1:2, and 1:1 Pd:Cu on alumina catalyst) suggesting the presence of Cu 2+ [24]. Moreover, the satellite peak is also observed in reduced Cu/Al2O3 indicating that the sample is not completely reduced, possibly due to the reduction condition and the oxidation by air when transferring the samples to XPS.…”
Abstract:The Pd and Pd-Cu on alumina catalysts were tested for hydrogenation of vinyl acetylene in mixed C4 in a circulating tubular reactor. The results showed that adding proper amounts of Cu improved the reaction activity, but inhibited 1,3-butadiene selectivity. Moreover, the presence of Cu retarded the carbon deposition on catalysts during the reaction. Temperature programmed oxidation (TPO), Temperature programmed reduction (TPR), H 2 chemisorption, and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the catalysts. The characterization suggested both geometric and electronic modifications.
“…In addition, weak Cu 2p3/2 satellite peak are also observed at around 10 eV higher (B.E. about 940-945 eV) for the CuO/Al2O3, and copper-rich sample (1:4, 1:2, and 1:1 Pd:Cu on alumina catalyst) suggesting the presence of Cu 2+ [24]. Moreover, the satellite peak is also observed in reduced Cu/Al2O3 indicating that the sample is not completely reduced, possibly due to the reduction condition and the oxidation by air when transferring the samples to XPS.…”
Abstract:The Pd and Pd-Cu on alumina catalysts were tested for hydrogenation of vinyl acetylene in mixed C4 in a circulating tubular reactor. The results showed that adding proper amounts of Cu improved the reaction activity, but inhibited 1,3-butadiene selectivity. Moreover, the presence of Cu retarded the carbon deposition on catalysts during the reaction. Temperature programmed oxidation (TPO), Temperature programmed reduction (TPR), H 2 chemisorption, and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the catalysts. The characterization suggested both geometric and electronic modifications.
This work reports the individual role of strong Lewis base sites on catalytic conversion of glucose hydrogenolysis to acetol/lactic acid, including glucose isomerisation to fructose and pyruvaldehyde rearrangement/hydrogenation to acetol/lactic acid. La2O3, Nd2O3, Sm2O3, and Pr6O11 were selected as representative oxides consisting of different base sites. The basicity of these lanthanide oxides was characterised by CO2‐TPD and DRIFT spectroscopy. It was found that lanthanide cation‐oxygen pairs, Brønsted OH group coordinated with one Lanthanide cation, and lanthanide cation near lanthanide cation‐oxygen pairs are the dominant base sites as compared to the other base sites on La2O3, Nd2O3, Sm2O3 and Pr6O11. In addition, the relative concentration of the base sites is different over the examined lanthanide oxides. These unique properties of lanthanide oxides are used to understand the individual role of base sites on the reactions mentioned above. Then, the catalytic results were correlated with the base properties of these lanthanide oxides. Based on this correlation, the base site requirements for each reaction were identified. In this regard, Brønsted OH group coordinated with one Lanthanide cation over Nd2O3 is found to be the suitable base site for glucose isomerisation. On the other hand, lactic acid is produced as the main product in glucose hydrogenolysis over lanthanide cation near lanthanide‐oxygen pairs on Pr6O11. Finally, lanthanide‐oxygen pairs over La2O3 are suitable base sites for retro‐aldol condensation of fructose to C3 chemicals.
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