Yizhuo Han

Novel reaction route for dimethyl carbonate synthesis from CO2 and methanol

Abstract Direct synthesis of dimethyl carbonate from CO 2 and methanol was investigated at near supercritical conditions using nickel acetate as the catalyst. It was demonstrated that dimethyl carbonate could be produced as the unique product at such low temperature as 305 K and the yield was 12 times higher than that at non-supercritical conditions. The synthesis was sensitive to the reaction pressure and showed a maximum for DMC yield at the ressure of 9.3 MPa. The concentration of methanol showed an obvious influence on both the yield and selectivity of DMC. Nickel acetate appeared to be the precursor of the catalyst. The formation mechanism of dimethyl carbonate in supercritical phase was proposed.

Methanation of syngas over coral reef-like Ni/Al2O3 catalysts

Abstract Coral reef-like Ni/Al 2 O 3 catalysts were prepared by co-precipitation of nickel acetate and aluminium nitrate with sodium carbonate aqueous solution in the medium of ethylene glycolye. Methanation of syngas was carried out over coral reef-like Ni/Al 2 O 3 catalysts in a continuous flow type fixed-bed reactor. The structure and properties of the fresh and used catalysts were studied by SEM, N 2 adsorption-desorption, XRD, H 2 -TPR, O 2 -TPO, TG and ICP-AES techniques. The results showed that the coral reef-like Ni/Al 2 O 3 catalysts exhibited better activity than the conventional Ni/Al 2 O 3 -H 2 O catalysts. The activities of coral reef-like catalysts were in the order of Ni/Al 2 O 3 -673> Ni/Al 2 O 3 -573> Ni/Al 2 O 3 -473> Ni/Al 2 O 3 -773. Ni/Al 2 O 3 -673-EG catalyst showed not only good activity and improved stability but also superior resistance to carbon deposition, sintering, and Ni loss. Under the reaction conditions of CO/H 2 (molar ratio) = 1:3, 593 K, atmospheric pressure and a GHSV of 2500 h −1 , CH 4 selectivity was 84.7%, and the CO conversion reached 98.2%.

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.

Cycloaddition between propylene oxide and CO2 over metal oxide supported KI

A novel catalyst system composed of KI supported on metal oxides for cycloaddition of propylene oxide with CO2 was investigated. It was found that the activity of KI for cycloaddition was strongly enhanced by ZnO as both support and promoter, resulting in a high yield of propylene carbonate within a short reaction time. Based on the characterization of BET, XRD, TG, IR and XPS-AES, this enhancement could be attributed to both the interaction between KI and amphoteric ZnO, which gave rise to the concerted active Lewis acid–base pairs of Iδ-Mδ+ and Kδ+O-δ and the dispersion of KI on the surface of the supports. The catalytic mechanism was then proposed.

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.

Selective oxidation of dimethyl ether to methyl formate over trifunctional MoO3–SnO2 catalyst under mild conditions

Dimethyl ether oxidation was conducted over MoO3–SnO2 catalysts prepared from different Sn salt precursors. Over the MoO3–SnO2 catalyst prepared from SnCl4, methyl formate selectivity reached 94.1% at 433 K without the formation of COx. The performance of the catalyst was determined by the existence form of MoO3 and the different surface bonding of Mo and O of the catalyst.

Rhenium oxide-modified H3PW12O40/TiO2 catalysts for selective oxidation of dimethyl ether to dimethoxy dimethyl ether

An efficient rhenium oxide-modified H3PW12O40/TiO2 catalyst is found for a new synthesis of dimethoxy dimethyl ether from dimethyl ether oxidation. The effects of Re loading, H3PW12O40 content and different feedstocks on the performance of Re–H3PW12O40/TiO2 were investigated. The results showed that DMM2 selectivity was significantly improved up to 60.0%, with 15.6% of DME conversion over 5% Re–20% H3PW12O40/TiO2. NH3-TPD, NH3-IR, Raman spectra, H2-TPR, XPS and TEM were used to extensively characterize the structure and surface properties of the catalysts. The introduction of H3PW12O40 significantly affected the structure and reducibility of surface rhenium oxide species, in addition to increasing the acidity of the catalyst. The increased number of Lewis acid sites and weak acid sites and the optimal ratio of Re4+/Re7+ of Re–H3PW12O40/TiO2 were favorable for the formation of DMM2 from DME oxidation. The possible reaction pathway of DME oxidation to DMM2 was proposed.

Mesoporous ZnZSM-5 zeolites synthesized by one-step desilication and reassembly: a durable catalyst for methanol aromatization

Mesoporous ZnZSM-5 zeolites were synthesized by introducing zinc directly into an alkaline and surfactant solution. The characterizations reveal that the presence of CTAB is favorable for the recrystallization of zeolite structural units. The amount of strong acid sites of mesoporous zeolites decreased, while the amount of medium acid sites of mesoporous zeolites (especial zinc-containing) increased. The amount of Lewis acid sites increased while the amount of Bronsted acid sites obviously decreased. For mesoporous ZnZSM-5, the emergence of a new species (ZnOH+) further increased the amount of Lewis acid sites. Both the external surface area and mesopore volume of mesoporous ZnZSM-5 gradually decreased with increasing zinc content. Most of zinc species introduced during desilication and reassembly dispersed on the surface of zeolites, but the addition of zinc species had no obvious influence on the zeolite morphology. The catalytic performance of the obtained materials was investigated via aromatization of methanol. The results show that BTX (benzene, toluene, and xylene) selectivity over mesoporous ZnZSM-5 gradually increases with increasing zinc content, and is much higher than that of mesoporous HZSM-5. However, the BTX selectivity of mesoporous HZSM-5 is obviously lower than that of HZSM-5 due to its much lower strong acid sites and larger pore size. The strong Bronsted acid sites, the Zn-Lewis acid sites and mesoporous channels have a synergistic effect on methanol aromatization over mesoporous ZnZSM-5 catalysts. Additionally, compared with HZSM-5, improvement in catalyst lifetime of MHZSM-5 and MZnZSM-5-2 is achieved by introducing additional mesoporous channels and decreasing the amount of strong acid sites.

Study on deactivation of hybrid catalyst for dimethyl ether synthesis in slurry reactor

Abstract Deactivation of composite catalyst for one-step dimethyl ether (DME) synthesis in slurry reactor was studied under reaction conditions of 260°C and 5.0 MPa. It was found that instability of Cu-based methanol synthesis catalyst led to rapid deactivation of the composite catalyst. Deactivation rate of the Cu-based catalyst in slurry reactor was compared with that in fixed-bed reactor. The results indicated that harmfulness of water, which is formed in the synthesis of DME, caused the Cu-based catalyst to deactivate at a high rate in slurry reactor. Techniques of TPR, XRD, and SEM-EDS were used to characterize the reduction behaviors, crystal structures, and surface properties of the catalyst. The results showed that carbon deposition and grain growth of Cu were important reasons for the rapid deactivation of the Cu-based catalyst, and no obvious metal loss of Cu was found.

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.