Tuning the product selectivity of dimethyl oxalate hydrogenation over WO_(x) modified Cu/SiO_(2) catalysts

Product selectivity and reaction pathway are highly dependent on surface structure of heterogeneous catalysts.For vapor-phase hydrogenation of dimethyl oxalate(DMO),"EG route"(DMO→methyl glycolate(MG)ethylene glycol(EG)→ethanol(ET))and"MA route"(DMO→MG→methyl acetate(MA))were proposed over traditional Cu based catalysts and Mo-based or Fe-based catalysts,respectively.Herein,tunable yield of ET(93.7%)and MA(72.1%)were obtained through different reaction routes over WO_(x) modified Cu/SiO_(2) catalysts,and the corresponding reaction route was further proved by kinetic study and in-situ DRIFTS technology.Mechanistic studies demonstrated that H_(2) activation ability,acid density and Cu-WO_(x) interaction on the catalysts were tuned by regulating the surface W density,which resulted in the different reaction pathway and product selectivity.What's more,high yield of MA produced from DMO hydrogenation was firstly reported with the H_(2) pressure as low as 0.5 MPa.

Synthesis of Methyl Glycolate by Hydrogenation of Dimethyl Oxalate over Cu-Ag/SiO_2 Catalyst

Methyl glycolate is a good solvent and can be used as feedstock for the synthesis of some important organic chemicals. Catalytic hydrogenation of dimethyl oxalate （DMO） over copper-silver catalyst supported on silica was studied. The Cu-Ag/SiO2 catalyst supported on silica sol was prepared by homogeneous deposition-precipitation of the mixture of aqueous euprammonia complex and silica sol. The proper active temperature of Cu-Ag/SiO2 catalyst for hydrogenation of DMO was 523-623 K. The most preferable reaction conditions for methyl glycolate （MG） were optimized： temperature at 468-478 K, 40-60 mesh catalyst diameter, H2/DMO ratio 40, and 1.0 h^-1 of LHSV.

Effect of copper loading on texture,structure and catalytic performance of Cu/SiO_2 catalyst for hydrogenation of dimethyl oxalate to ethylene glycol

Cu/SiO2 catalysts prepared by a convenient and efficient method using the urea hydrolysis deposition-precipitation （UHDP） technique have been proposed focusing on the effect of copper loading.The texture,structure and composition are systematically characterized by ICP,FTIR,N 2-physisorption,N2O chemisorption,TPR,XRD and XPS.The formation of copper phyllosilicate is observed in Cu/SiO2 catalyst by adopting UHDP method,and the amount of copper phyllosilicate is related to copper loading.It is found the structure properties and catalytic performance is profoundly affected by the amount of copper phyllosilicate.The excellent catalytic activity is attributed to the synergetic effect between Cu0 and Cu ＋.DMO conversion and EG selectivity are determined by the amount of Cu0 and Cu＋,respectively.The proper copper loading （30 wt%） provides with the highest ratio of Cu ＋ /Cu0,giving rise to the highest EG yield of 95% under the reaction conditions of p=2.0 MPa,T=473 K,H2/DMO=80 and LHSV=1.0h-1.

Paired-Pd(Ⅱ) centers embedded in HKUST-1 framework: Tuning the selectivity from dimethyl carbonate to dimethyl oxalate

CO oxidative coupling to dimethyl oxalate(DMO) is the most crucial step in coal to ethylene glycol. Pdbased supported catalysts have been verified effective for generating DMO, but concomitant generation of dimethyl carbonate(DMC) is always unavoidable. It is generally accepted that Pd(0) is the active species for producing DMO, while Pd(II) for DMC. However, density functional theory calculations have proposed that the selectivity to DMO or DMC highly depends on the space state of Pd species rather than its oxidative state. It is thus urgently desired to develop high-efficient catalysts with well-defined structure,and further to elucidate the structure-performance relationship. In this work, HKUST-1 with unique structure of paired-Cu(Ⅱ) centers was chosen as ideal support to construct the catalysts with respective paired-Pd(Ⅱ) centers and isolated-Pd(Ⅱ) centers via in situ Pd species doping. In despite of featuring Pdδ+(δ≈2) oxidation state, the synthesized paired-Pd(Ⅱ)/HKUST-1 catalyst still exhibited DMO as dominant product(90.8% of DMO selectivity). For isolated-Pd(Ⅱ)/HKUST-1 catalyst, however, the main product was DMC(84.8% of DMC selectivity). Based on catalyst characterizations, the structures of paired-Pd(Ⅱ) centers and isolated-Pd(Ⅱ) centers were determined. DMO was generated from the coupling of adjacent *COOCH;intermediates adsorbed on paired-Pd(Ⅱ) centers, while DMC was produced from the reaction between methyl nitrite and the *COOCH;intermediates formed on isolated-Pd(Ⅱ) centers. Current work is the first MOFs-based catalyst with well-defined structure being applied in CO oxidative coupling reaction, which not only sheds light on the structure-performance relationship, but also inspires the potential of using MOFs as tunable platform to design high-efficient catalysts in heterogeneous catalysis.

Catalytic Performance and Texture of TEOS Based Cu/SiO_2 Catalysts for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Highly active and selective Cu/SiO2 catalysts for hydrogenation of dimethyl oxalate（DMO） to ethylene glycol（EG） were successfully prepared by means of a convenient one-pot synthetic method with tetraethoxysi lane（TEOS） as the source of silica. XRD, H2-TPR, SEM, TEM, XRF and N2 physisorption measurements were performed to characterize the texture and structure of Cu/SiO2 catalysts with different copper loadings. The active components were highly dispersed on SiO2 supports. Furthermore, the coexistence of Cu0 and Cu＋ contributed a lot to the excellent performance of Cu-TEOS catalysts. The DMO conversion reached 100% and the EG selectivity reached 95% at 498 K and 2 MPa with a high liquid hourly space velocity over the 27-Cu-TEOS catalyst with an actual cop per loading of 19.0%（mass fraction）.

Preparation of Diphenyl Oxalate from Transesterification of Dimethyl Oxalate with Phenol over TS-1 Catalyst

Diphenyl oxalate was synthesized from transesterification of dimethyl oxalate with phenol over TS-1 ( 2.5 wt% Ti ) catalyst. TS-1 catalyst, as a heterogeneous catalyst, showed excellent selectivity of diphenyl oxalate and methylphenyl oxalate compared with other homogeneous catalysts. Lewis acid sites on TS-1 catalyst were the active sites for transesterification of dimethyl oxalate with phenol. The high selectivity was closely related to the weak acid sites over TS-1.

In situ IR study of dimethyl oxalate hydrogenation to ethylene glycol over Cu/SiO_2 catalyst

The mechanism of dimethyl oxalate hydrogenation to ethylene glycol over Cu/SiO2 catalyst was investigated by in situ Fourier transform infrared （FTIR） spectroscopy. It was found that dimethyl oxalate and methyl glycolate proceeded via dissociative adsorption on Cu/SiO2 catalyst, and four main intermediates, CH3OC（O）（O）C-M （1655 cm-1）, M-C（O）（O）C-M （1618 cm-1）, HOCH2（O）C--M （1682 cm-1） and CH3O-M （2924-2926 cm-1）, were identified during the reaction. It was concluded that dimethyl oxalate hydrogenation to ethylene glycol mainly proceeded along the route： dimethyl oxalate ／rightarrow CH3OC（O）（O）C-M → methyl glycolate →HOCH2（O）C-M → ethylene glycol. Finally a schematic reaction network was proposed.

Heterogeneous Cu_2O-mediated ethylene glycol production from dimethyl oxalate

An efficient process for the conversion of dimethyl oxalateinto ethylene glycol with high selectivity and high yield over CuO was investigated. In situ formed Cu as a true catalytically active species showed a good catalytic performance for DMO conversion to produce EG in 95% yield.

Effects of ethanol on the in situ synthesized Cu/SiO_2 catalyst:Texture,structure,and the catalytic performance in hydrogenation dimethyl oxalate to ethylene glycol

The Cu/SiO_2 catalysts were in situ synthesized by the hydrolysis of tetraethyl orthosilicate（TEOS） in one phase solution using ethanol as co-solvent or TEOS/H_2O two phases solution,followed by the precipitation of copper on SiO_2 by ammonia evaporation. In the hydrogenation of dimethyl oxalate,the catalyst prepared by one phase hydrolysis exhibited higher activity and ethylene glycol（EG） selectivity at lower temperature than that of two phases due to its larger BET surface area and multimodal pore distribution.At 488-503 K,the catalyst prepared in one phase solution with water/ethanol（W/E） volume ratio of 3：1 exhibited 90- 95%EG selectivity,while catalyst prepared by two phase hydrolysis reached 90%EG selectivity only at 498-503 K.

Pd-Fe/a-AI203/cordierite monolithic catalysts for the synthesis of dimethyl oxalate： effects of calcination and structure

Cordierite monoliths coated with Pd-Fe/a- Al2O3 catalysts were prepared at various calcination temperatures and characterized by thermogravimetry, temperature-programmed reduction, transmission electron microscopy, diffuse reflectance infrared Fourier transfor- mation spectroscopy and X-ray diffraction. The performance of the catalytic monoliths for the synthesis of dimethyl oxalate （DMO） through a CO coupling reaction was evaluated. Monolithic catalysts with calcination temperatures ranging from 473 K to 673 K exhibited excellent dispersion of Pd, good CO adsorption properties, and excellent performance for the coupling reaction. The optimized monolithic catalyst exhibited a much higher Pd efficiency （denoted as DMO （g）.Pd （g）-1 h 1） （733h-1） than that of the granular catalyst （60.2 h-1）, which can be attributed to its honeycomb structure and the large pore sizes in the a-Al2O3 washcoat which was accompanied with an even distribution of the active component in the coating layer along the monoliths channels.

A Simple and Highly Efficient Preparation of Structurally Diverse Aryl β-diketoacids as HIV-1 Integrase Inhibitors

In order to provide a facile and practical access to structurally diverse aryl -diketoacids, An improved and highly efficient oxalylation method was developed which employed commercially available and cheap reagents. The oxalylation of aryl methyl ketones, the key step to construct the pharmacophore of aryl -diketoacids, was con-siderably facilitated by a new combination of dimethyl oxalate as an oxalic source and sodium tert-butoxide as a base. A wide variety of aryl -diketoacids bearing different functional groups can be prepared rapidly in high yields at room temperature with this method, which has significant advantages over the previously reported procedures in a wider application range, much less amount of reagents, pretty higher yields and quite shorter reaction time. The bis-aryldiketoacids 3k and 3l, readily prepared by this method, displayed interesting and promising inhibitory ac-tivities against HIV-1 integrase and HIV-1 replication in cells.