Yingquan Wu

The mechanism of higher alcohol formation on ZrO2-based catalyst from syngas

A chain growth scheme for the synthesis of alcohols from carbon monoxide and hydrogen is proposed based on the chemical enrichment method on ZrO2-based catalyst. Methanol addition has no obvious effect on the STY of C2+ alcohols, indicating that COH→CCOH is a slow initial growth step. Addition of ethanol and propanols can enhance the STY of isobutanol, especially n-propanol, revealing that n-propanol is largely the precursor of isobutanol. Results of large alcohols addition further reveal the relationship between small alcohols and large alcohols of formation. Also, addition of aldehydes has a similar effect on the formation of higher alcohols, indicating that alcohols exist in the form of aldehydes before desorption. Anisole are introduced into syngas for confirmation of predicted intermediates and the result indicates that formyl species is participated both in the formation of methanol and higher alcohols. Reaction temperature has a significant effect on the chain growth of alcohols synthesis. Under low temperature, chain growth occurs with CO insertion and alcohols are linear products. Isobutanol appears and becomes the main product during C2+ alcohols undergo an aldo-condensation reaction at high temperature.

The role of potassium promoter in isobutanol synthesis over Zn–Cr based catalysts

A series of Zn–Cr oxide nanoparticles with different contents of potassium promoter is obtained by coprecipitation and post-calcination methods. Transmission Electron Microscopy (TEM), Powder X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FT-IR) were used to confirm the structure of the different Zn–Cr oxides. The results demonstrate that the potassium promoter would tailor the microstructure of the Zn–Cr spinel by affecting the cation distribution between the tetrahedral and octahedral vacancies. Furthermore, the potassium promoter also affects tremendously the state of the oxygen species on the surface over the Zn–Cr spinel. Both the population and stability of the oxygen species could be enhanced by the potassium promoter. In addition, the surface hydroxyl species could facilitate the formation of formate, which is a very significant intermediate C1 species for alcohol synthesis. The catalyst activity and isobutanol selectivity are closely related to the content of the potassium promoter, clearly demonstrating that the potassium promoter should be one of the crucial factors to consider to enhance the catalytic performance for isobutanol formation over the Zn–Cr catalysts.

The real active sites over Zn–Cr catalysts for direct synthesis of isobutanol from syngas: structure-activity relationship

A series of Zn–Cr oxides nanoparticles were prepared by a coprecipitation procedure. The structure of different catalysts was investigated by X-ray Absorption Fine Structure (XAFS), X-ray photoelectron spectroscopy (XPS), temperature programed reduction of hydrogen (H2-TPR) and in situ infrared spectrum (in situ IR). Both EXAFS and XANES demonstrated the cation disorder distribution became more serious with decreasing annealing temperature and increasing Zn/Cr molar ratios. The cation distribution also affected the oxygen state on the surface over Zn–Cr spinel. The population of surface hydroxyl species increased with more serious cation disorder distribution and they facilitated the formate formation which was a significant intermediate C1 species for alcohol synthesis. This study was the first time to investigate the situation of cation distribution in Zn–Cr spinel by XAFS and related it to catalyst performance. The results revealed that the isobutanol productivity presented a linear relationship to the level of cation disorder distribution in Zn–Cr spinel, unambiguously revealing the real active sites and structure-activity relationship.

Ti-SBA-15 supported Cu–MgO catalyst for synthesis of isobutyraldehyde from methanol and ethanol

Ti-SBA-15 supported Cu and MgO catalysts were prepared and used for the first time in the one-step conversion of methanol and ethanol to isobutyraldehyde (IBA). The results show that the loadings of Cu and MgO, and catalyst calcination temperature have strong effects on the catalyst activity. A high yield of IBA, 32.7%, and high ethanol conversion, 96.6%, were achieved at 360 °C with WHSV of 3.0 mL (g−1 h−1) on the catalyst calcined at 400 °C when the loadings of Cu and Mg were 20.0 wt% and 6.5 wt%, respectively. The physicochemical properties of the catalysts were analyzed by various techniques including XRD, N2 adsorption and desorption, FT-IR, H2-TPR, CO2-TPD and XPS. The ordered mesoporous structure of the catalysts was retained with the introduction of CuO and MgO. The size of CuO particles on the catalysts was retained though they suffered from a varied calcination temperature. H2-TPR measurements revealed that the increase of calcination temperature from 400 °C to 700 °C resulted in the decrease of basicity of the catalysts, and enhanced the interaction between the Cu and Mg species and the support. The results from XPS analysis indicated that the binding energy of Cu 2p was increased with the introduction of MgO, while the increased calcination temperature easily resulted in the decrease of Cu content on the catalyst surface due to probable migration of Cu species into internal pores or their incorporation into the framework of the Ti-SBA-15 support.

Binary ZnO/Zn–Cr nanospinel catalysts prepared by a hydrothermal method for isobutanol synthesis from syngas

A series of binary ZnO/Zn–Cr nanospinel catalysts were prepared by a hydrothermal method and applied in direct synthesis of isobutanol from syngas, during which the effect of the hydrothermal time/temperature on the catalytic performance in the isobutanol synthesis has been investigated at 400 °C and 10 MPa. The catalysts were characterized by XRD, N2 adsorption–desorption, TPR, TPD, FT-IR spectroscopy, XPS, XRF, SEM and TEM. The XRD and TEM results show that the binary ZnO/Zn–Cr nanospinel structure forms well by the hydrothermal method. Compared with other ZnCr catalysts, the catalyst prepared under the hydrothermal conditions of 16 h and 160 °C has the largest BET area with the largest amount of active sites, leading to a high total alcohol production rate (TAPR). Meanwhile, the surface Zn/Cr molar ratio (1.27) and K content (1.64%) on the ZnCr-16-160 catalyst are higher. The enrichment phenomenon of Zn on the catalyst surface could improve the interaction between ZnO and a non-stoichiometric Zn–Cr spinel, forming a ZnO layer mixed with the Zn–Cr spinel. Since K is known as a C-chain increasing promoter, the high K content is helpful in improving the total alcohol and isobutanol selectivity. Thus, the appropriate hydrothermal time and temperature for the binary ZnO/Zn–Cr catalyst preparation are 16 h and 160 °C, respectively, and the best catalytic performance is obtained on the ZnCr-16-160 catalyst with a total alcohol selectivity of 60.2% and an isobutanol distribution of 27.0 wt%.