Hongjuan Xie

Modification of Cu-based methanol synthesis catalyst for dimethyl ether synthesis from syngas in slurry phase

The bifunctional catalyst with activity for methanol dehydration and water-gas shift reaction was prepared by impregnating γ-alumina with Cu(NO 3) 2 dissolved in water, acetone and glycol, respectively. The catalyst was characterized by means of H 2-TPR, XRD and NH 3-TPD for investigating its reduction properties, crystal structure and acidic sites. The results showed that the catalyst sample prepared by using glycol as the dispersion solvent had a large amount of reducible copper oxide. Copper oxide did not disperse uniformly on the catalyst sample prepared in water solvent and part of copper oxide existed in Cu and Cu-Al compounds, while copper oxide dispersed uniformly on the catalyst sample prepared in glycol or acetone solvent. The dispersion of weak acid sites was more concentrative over the catalyst sample prepared in glycol solvent. The modified dehydration catalyst could increase CO conversion and dimethyl ether selectivity and restrain side reactions. When the organic solvent was used to prepare the modified catalyst, there was no obvious effect on CO conversion, but the dimethyl ether selectivity was improved and side reactions were depressed evidently because of the change in surface acidity.

A highly efficient Ga/ZSM-5 catalyst prepared by formic acid impregnation and in situ treatment for propane aromatization

A simple method for the preparation of a Ga/ZSM-5 catalyst for propane aromatization was established by formic acid impregnation and in situ treatment. The catalyst prepared by this novel method showed remarkably superior activity of propane aromatization. Under the conditions T = 540 °C, P = 100 kPa, WHSV = 6000 ml g−1·h−1 and with a N2/C3H8 molar ratio of 2, the highest propane conversion and selectivity to BTX (benzene, toluene and xylene) achieved on H–Ga/SNSA catalyst was 53.6% and 58.0%, respectively, much higher than that of the catalyst prepared using the traditional impregnation method (38.8% and 48.2%). The catalysts were characterized by nitrogen physical adsorption, ICP-AES, DRIFT, py-FTIR, NH3-TPD, H2-TPR, XPS and 27Al MAS NMR techniques. The characterization data indicated that this facile methodology enhanced the dispersion of the Ga species and promoted the formation of highly dispersed (GaO)+ species, which could exchange with the acidic protons (Bronsted acid sites) of the zeolite framework, contributing to the strong Lewis acidity. The super catalytic behavior was attributed to the synergistic effect between the strong Lewis acid sites generated by the (GaO)+ species and the Bronsted acid sites.

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.

Effects of reaction atmosphere on dimethyl ether conversion to propylene process over Ca/ZSM-5

Abstract Effects of reaction atmospheres (nitrogen, carbon monoxide, carbon dioxide, syngas and water vapor) on stability of the catalyst, selectivities to propylene and byproducts for dimethyl ether conversion to propylene (DTP) over Ca/ZSM-5 were investigated in a continuous flow fixed-bed reactor. Besides, the regenerated catalyst was also studied for DTP process. The results show that the catalyst exhibits best stability, highest propylene selectivity and lowest selectivities to byproducts in carbon dioxide atmosphere, followed by nitrogen, carbon monoxide and syngas atmosphere, and water vapor atmosphere exerts worst effect on DTP. The catalytic performance of the regenerated catalyst also demonstrates that carbon dioxide as reaction atmosphere is most beneficial to DTP process.

Tri-reforming of coal bed methane to syngas over the Ni-Mg-ZrO2 catalyst

Abstract Ni-ZrO 2 and Ni-Mg-ZrO 2 catalysts were prepared by a co-precipitation method, and then were characterized by BET, XRD, H 2 -TPR and CO 2 -TPD techniques. The performances of catalysts in the tri-reforming of coal bed methane to syngas were studied in a fixed bed reactor. The reaction conditions (temperature and feed gas composition) were mainly investigated. The results showed that at t =800°C, atmospheric pressure, CH 4 /CO 2 /H 2 O/O 2 /N 2 =1.0/0.45/0.45/0.1/0.4, GHSV=30000 mL·g −1 ·h −1 , about 99% of CH 4 conversion, 65% of CO 2 conversion, and V H2 / V CO of 1.5 could be achieved during 58 h of reaction, which are related to the strong metal-support interaction, the good thermal stability and basic nature of the catalyst. Furthermore, high temperature favors the tri-reforming of methane. By adjusting the feed gas composition, a specific V H2 / V CO could be achieved.

Effect of calcination temperature on performance of K-Cu/Zn/La/ZrO2 for isobutanol synthesis

Abstract In this paper, the K-promoted Cu/Zn/La/ZrO2 catalysts were prepared by co-precipitation methods, and the hydrogenation of CO was used as the probe reaction to investigate the catalytic performance. The structure and surface properties of K-Cu/Zn/La/ZrO2 catalysts were characterized by XRD, TG, BET, NH3-TPD, H2-TPR, Raman and XPS techniques respectively. The results indicated that the relationship between the structure, specific surface and catalyst activity was not significant, and the strong acidic sites of catalyst surface were not suitable for the formation of isobutanol. But the results indicated that the synergy among Cu-Zn-Zr would have an important effect on the activity of K-Cu/Zn/La/ZrO2 catalysts. When the calcinations temperature was 450°C, the synergistic effect of Cu-Zn-Zr was strongest so that the CuO could be reduced easily. Under the optimum calcination temperature, the conversion of CO reached 69.47%, the selectivity of isobutanol approached 19.09%, and the primary products were methanol and isobutanol that was 95.02% of the alcohol products.

Mechanistic insight to acidity effects of Ga/HZSM-5 on its activity for propane aromatization

Ga-modified HZSM-5 precursors, containing 1 wt% Ga, were first prepared using the incipient wetness impregnation method, and then subjected to one or three-times consecutive treatment by cycles of reduction in hydrogen and re-oxidation in air. The resulting Ga/HZSM-5 catalysts were characterized by N2 physical adsorption, ICP-AES, DRIFT, Py-FTIR, NH3-TPD, H2-TPR, XPS, DRIFT-TPSR and MS-TPSR techniques to obtain clear mechanistic details that the acidity of these Ga/HZSM-5 catalysts affected their activity for propane aromatization. The characterization data suggested that the impregnated introduction of Ga to ZSM-5 zeolite and subsequent reduction–oxidation treatment led to a great decrease in the number of Bronsted acid sites (BAS) and promoted the formation of strong Lewis acid sites (LAS) attributed to highly dispersed Ga species. The formed strong LAS specifically promoted the dehydrogenation steps during propane aromatization, whereas the original BAS were responsible for the whole aromatization process. The TPSR results suggested that propane was converted to propylene through the dehydrogenation on BAS and strong LAS, and simultaneously converted to ethylene through the β-scission on BAS at a low temperature. With the elevation of temperature, the generated propylene and ethylene on the strong BAS and the strong LAS were further converted into BTX aromatics accompanied by hydrogen release. It was plausible that the highly efficient synergy between BAS and strong LAS could result in lower aromatization temperatures and more product of benzene (β state) over the Ga/HZSM-5 catalysts than that over the Ga-modified HZSM-5 precursors.

Netted structure of grain boundary phases and its influence on electrical conductivity of Cu- Ni-Si system alloys

Abstract Cu–Ni–Si alloys with four different Cu contents were fabricated by means of smelting. Subsequently, isothermal aging and hot rolling followed by aging treatment were carried out. The microstructure and phase composition were characterised by optical microscope, transmission electron microscope and X-ray diffractometer. Electrical conductivity was measured by using an eddy current based technique. The results show that the electrical conductivities of as cast Cu–Ni–Si alloys decrease obviously with a decline in Cu content. Isothermal aging is favourable to enhance the electrical conductivities of Cu–Ni–Si alloys with higher than 90%Cu content rather than that with <90%Cu content containing an integrated netted structure of grain boundary phases. The electrical conductivities of as rolled Cu–Ni–Si alloys can obviously be increased by subsequent aging treatment. The above results suggest that the disintegration of the integrated netted structure at the grain boundary is a promise to achieve high electrical conductivity for Cu–Ni–Si alloys.