Selective Hydrogenation Of Dimethyl Oxalate Research Articles

Facile synthesis of Cu@Ag/SiO2 catalysts for the selective hydrogenation of dimethyl oxalate to methyl glycolate

A promising route for producing biodegradable polyglycolic acid material from syngas has garnered increasing attentions. In this route, one of the pivotal issues is developing favorable catalysts for semi-hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG). Silver catalysts were reported to be effective but suffered from the high cost. Herein, we prepared small-sized Cu@Ag/SiO2 catalysts with appropriate Ag/Cu ratios by a facile wet impregnation method. This core–shell structure facilitated the intermetallic electronic transference from Cu to Ag. The surface exposure of electron-rich silver species could promote the catalytic activity and MG desorption in the DMO hydrogenation, which achieved high efficiency without compromising the MG selectivity. The optimal catalyst with Ag/Cu mass ratio of 3/2 displayed excellent space time yield towards MG of 47.3 g·gAg−1·h−1. These insights could offer a potential strategy to reduce the silver-based catalyst cost for the semi-hydrogenation of DMO to MG.

Engineering an egg-shell structure for the Ag/SiO2 pellet catalyst for selective hydrogenation of dimethyl oxalate to methyl glycolate

An egg-shell-type Ag/SiO2 pellet catalyst with an optimized thickness of the Ag-shell exhibits both enhanced activity and selectivity for DMO hydrogenation to MG.

A solid-state synthetic strategy toward nickel-based bimetallic interstitial compounds (MNi3Cx, M = Zn, In, Ga).

Bimetallic interstitial compounds with unique geometric properties have attracted increasing attention in energy-related fields and diverse chemical transformations. Current synthesis of these compounds generally involves at least one wet-chemistry step with the use of various solvents to prepare the bimetallic precursors, and no universal protocols for different compositions are yet available. Herein, a novel synthetic strategy toward a platform of nickel-based bimetallic interstitial compounds with the formula MNi3Cx, M = Zn, In, and Ga, was developed based on a straightforward solid-state transformation, i.e., simply annealing the hydroxides of the respective metals in the presence of different carbon precursors (cyanamide, dicyandiamide, melamine, and urea) in a hydrogen stream. The key process parameters influencing the compositions of the final products are studied and the formation mechanism is discussed based on advanced characterization techniques. Powder X-ray diffraction reveals MNi3Cx as a single phase and electron microscopy shows that the MNi3Cx particles are covered with N-doped carbon shells. Extrapolation to other bimetallic interstitial compounds failed when following the above protocol, and the successful examples are linked to the formation of the corresponding bimetallic alloys in the absence of carbon precursors. When evaluated for the selective hydrogenation of dimethyl oxalate, both InNi3C0.5 and ZnNi3C0.7 show comparable high activity. While ZnNi3C0.7 delivers the highest selectivity for methyl glycolate, tunable methyl glycolate and ethylene glycol are formed on InNi3C0.5. In general, this facile solvent-free strategy affords an interesting scaffold to fabricate more advanced multi-metallic interstitial compounds with broad applications.

Selective Hydrogenation of Dimethyl Oxalate to Methyl Glycolate over Boron-Modified Ag/SiO2 Catalysts.

The addition of boron (B) as a promoter to the Ag/SiO2 catalyst for the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was investigated. A comparison of the preparation method for incorporation of B found that the addition during the ammonia evaporation deposition-precipitation synthesis of the Ag/SiO2 catalyst (Ag-B/SiO2) was inferior to incipient wetness impregnation introduction of the Ag/SiO2 catalyst (B/Ag/SiO2). Moreover, the effects of B contents (0.5-5 wt %) on the physicochemical properties and catalytic performance of the B/Ag/SiO2 catalysts were investigated by XRF, N2-physisorption, XRD, FTIR, TEM, EDX mapping, H2-TPR, NH3-TPD, XPS, and catalytic testing. The results indicated that both the catalytic activity and stability of the Ag/SiO2 catalyst were noticeably enhanced after the introduction of B. The B/Ag/SiO2 catalyst with 1 wt % B showed the best catalytic performance of 100% DMO conversion and 88.3% MG selectivity, which could be attributed to the highest dispersion of the active metal and the smallest Ag particle size stabilized by the strong interaction between silver and boron species.

Regulating mesopore structures of support toward enhanced selective hydrogenation of dimethyl oxalate to methyl glycolate on Ag catalysts

Precisely regulating mesopore structures toward enhanced diffusion of reactants and targeted product is of great significance for achieving simultaneously improved activity and selectivity, which is exemplified by this work employing mesoporous silica with distinct structured mesopores as support for Ag catalysts to selectively hydrogenate dimethyl oxalate (DMO) into methyl glycolate (MG). Mesoporous silica nanosphere (MSNS) with center-radial pores shows shorter pore length than SBA-15 with parallel mesopores, which is beneficial for the diffusion process and thus gives rise to enhanced hydrogenation activity. Inspired by these insights, MSNSs sized in 50, 90, 120 and 160 nm are further synthesized to regulate pore length and systematically explore their effects on the reaction. The diffusion process is enhanced with decreasing the size of MSNS from 160 to 50 nm, as elucidated by the effective diffusion time constant (De/R2) determined by zero-length column (ZLC) method. Accordingly, DMO can facilely diffuse into the mesopores with shorter length to access the active sites while the formed MG product can easily diffuse out to avoid the over-hydrogenation process, which is corroborated by the comparison for performances of these Ag/MSNSs catalysts. Notably, a moderately short pore length, balancing well the diffusion and hydrogenation process, is more preferable for achieving both higher activity and better selectivity to MG, and MSNS sized in 90 nm supported Ag catalyst thus exhibits the greatest performances, with MG selectivity up to 96.6 % at 99.7 % of DMO conversion.

Ni-Modified Ag/SiO2 Catalysts for Selective Hydrogenation of Dimethyl Oxalate to Methyl Glycolate.

Ni-modified Ag/SiO2 catalysts containing 0~3 wt.% Ni were obtained by impregnating Ni species onto Ag/SiO2 followed by calcination and reduction. The catalysts’ performance in the hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was tested. Ag-0.5%Ni/SiO2 showed the highest catalytic activity among these catalysts and exhibited excellent catalytic stability. The effects of the Ni content on the structure and surface chemical states of catalysts were investigated by XRF, N2-sorption, XRD, TEM, EDX-mapping, FT-IR, H2-TPR, UV–vis, and XPS. The better catalytic activity and stability of Ni-modified Ag/SiO2 (versus Ag/SiO2) are ascribed to the improved dispersion of active Ag species as well as the higher resistance to the growth of Ag particles due to the presence of Ni species.

Atomic ruthenium stabilized on vacancy-rich boron nitride for selective hydrogenation of esters

Constructing and taming metal–support interaction of atoms and/or clusters has emerged as a promising protocol to maximize the catalytic performance of noble metal-based materials. Here, we report atomic ruthenium (Ru) with the oxidized state immobilized on defect-rich hexagonal boron nitride (d-BN) nanosheets and the essential interfacial electronic effect on Ru deduced from B- and N-vacancies for superior selective hydrogenation of esters. Experimental results indicate that strong electronic interplay exists between vacancies and atomic Ru species. Unlike defect-free commercial hexagonal BN (h-BN), d-BN can highly stabilize the active Ru species in atomic scale with oxidation state, and the obtained Ru/d-BN significantly increases the catalytic activity and durability. Specifically, the turnover frequency of Ru/d-BN is more than one order of magnitude higher than that of the conventional optimized Ag/SiO2 catalyst for the selective hydrogenation of dimethyl oxalate to methyl glycol. Systematic characterizations show that the Ru on B- and N-vacancies, and the defective BN serves as electron acceptor. The findings demonstrate the overall electronic effect on the electron-rich feature of Ru on d-BN, such that the electronic metal–support interactions cause the Ru species to favor the adsorption and selective scission of C–O bonds in esters, revealing a highly efficient hydrogenation catalysis.

Synthesis of methyl glycolate by hydrogenation of dimethyl oxalate with a P modified Co/SiO2 catalyst

A P-modified Co/SiO2 catalyst exhibited excellent performance in selective hydrogenation of dimethyl oxalate to methyl glycolate.

Highly selective hydrogenation of dimethyl oxalate to methyl glycolate and ethylene glycol over an amino-assisted Ru-based catalyst.

A Ru/NH2-MCM-41 catalyst was prepared via a coordination-assisted strategy for chemoselective hydrogenation of dimethyl oxalate with a high selectivity of methyl glycolate (ca. 100%) and ethylene glycol (>90%) at reaction temperatures of 343 K and 433 K, respectively. The amino groups help to anchor and form stable electron-rich Ru active sites, which accounts for the excellent CO bond activation and hydrogenation selectivity.

Boron Modified Bifunctional Cu/SiO2 Catalysts with Enhanced Metal Dispersion and Surface Acid Sites for Selective Hydrogenation of Dimethyl Oxalate to Ethylene Glycol and Ethanol.

Boron (B) promoter modified Cu/SiO2 bifunctional catalysts were synthesized by sol-gel method and used to produce ethylene glycol (EG) and ethanol (EtOH) through efficient hydrogenation of dimethyl oxalate (DMO). Experimental results showed that boron promoter could significantly improve the catalytic performance by improving the structural characteristics of the Cu/SiO2 catalysts. The optimized 2B-Cu/SiO2 catalyst exhibited excellent low temperature catalytic activity and long-term stability, maintaining the average EG selectivity (Sel.EG) of 95% at 190 °C, and maintaining the average EtOH selectivity (Sel.EtOH) of 88% at 260 °C, with no decrease even after reaction of 150 h, respectively. Characterization results revealed that doping with boron promoter could significantly increase the copper dispersion, enhance the metal-support interaction, maintain suitable Cu+/(Cu+ + Cu0) ratio, and diminish metallic copper particles during the hydrogenation of DMO. Thus, this work introduced a bifunctional boron promoter, which could not only improve the copper dispersion, reduce the formation of bulk copper oxide, but also properly enhance the acidity of the sample surface, so that the Cu/SiO2 sample could exhibit superior EG selectivity at low temperature, as well as improving the EtOH selectivity at high temperature.

Understanding size-dependent hydrogenation of dimethyl oxalate to methyl glycolate over Ag catalysts

Ag catalysts are promising for the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG), where the size of Ag nanoparticles strongly dominates their catalytic performances. Fundamental understandings on the size dependence, especially at the level of active sites, are still lacking but of great importance for the rational design of Ag-based catalysts for this reaction. Herein, a series of catalysts consisting of Ag nanoparticles sized from 2.9 to 8.8 nm anchored on amine-derivatized mesoporous silica nanospheres (Ag/AS) were synthesized and employed to understand the size-dependent DMO hydrogenation to MG. A volcano-shape trend between the hydrogenation activity and the increasing Ag particle size is observed for the differently sized Ag/AS catalysts, indicating a remarkable size dependence. The origin of the size dependence is further understood based on the cuboctahedron model of Ag nanoparticle, and the step-likes active sites are identified as the dominant ones. Results combining with the X-ray photoelectron spectroscopy, in situ Fourier transform infrared spectroscopy and temperature programmed desorption studies, indicate that the hydrogenation of DMO to MG on Ag/AS catalysts is mainly dominated by the number of active sites when the Ag particle size ≥ 5.3 nm, but by the electronic properties when the Ag particle size < 5.3 nm. The balance between the number of active sites and electronic structure gives rise to a maximal reaction rate in term of apparent TOF on the Ag/AS catalyst with Ag particle size of 5.3 nm. These understandings may guide the design of highly efficient Ag catalysts for the coal-based MG production.

Catalyst consisting of Ag nanoparticles anchored on amine-derivatized mesoporous silica nanospheres for the selective hydrogenation of dimethyl oxalate to methyl glycolate

Developing efficient catalysts for the selective hydrogenation of dimethyl oxalate (DMO) is of great significance for the coal-based production of methyl glycolate (MG), but designing processes for this conversion is challenging. Herein we report an unprecedented catalytic performance for the selective hydrogenation of DMO to MG, achieved by using a catalyst based on Ag nanoparticles anchored inside the mesopores of amine-derivatized silica nanospheres (NH2-MSNS). It was determined that the unique microenvironment endowed by the amine-derivatized channel surfaces helps this Ag catalyst promote the activation of DMO and H2 to yield MG with high selectivity, and also prevents sintering and coking, hence improving stability. Accordingly, the resulting Ag/NH2-MSNS catalyst was shown to be capable of promoting the hydrogenation reaction with a turnover frequency of 230 h−1 and a MG selectivity of 97% at nearly 100% of DMO conversion, a performance that was sustained for at least 250 h; these results are significantly better than those seen with other reported catalysts. Our study points to a promising route for the development of high-performing Ag catalysts to be used in the coal-based MG production.

Constructing copper-zinc interface for selective hydrogenation of dimethyl oxalate

The development of robust catalysts for selective hydrogenation of dimethyl oxalate (DMO) is key for the expansion of ethylene glycol (EG) production from C1 and renewable feedstocks. Copper-based catalysts promoted with Cr are industrially used, but it is desirable to develop more environmentally-benign alternatives. Silica-supported copper-zinc bimetallic catalysts featuring intimate metal contact are designed and used to establish the structure-performance relationships through combining in-depth characterizations with steady-state catalytic testing. Our study highlights: i) that the surface Cu0/Cu+ ratio is a reliable catalytic descriptor that determines the activity and selectivity, and ii) the importance of copper-zinc interface in stabilizing copper nanoparticles both under reduction and hydrogenation conditions. Controlled zinc doping allows fine tuning of these properties for the targeted reaction. Excellent performance has been achieved on the best-performing catalyst with >99.6% DMO conversion, >96.0% EG selectivity, and unprecedented stability of 800 h without catalyst deactivation, which represents a significant advance in the selective hydrogenations.

A boron-doped carbon aerogel-supported Cu catalyst for the selective hydrogenation of dimethyl oxalate

The modification of B in carbon support can modulate the hydrogenation selectivity.

Nanoporous Ni3P Evolutionarily Structured onto a Ni Foam for Highly Selective Hydrogenation of Dimethyl Oxalate to Methyl Glycolate.

Methyl glycolate (MG) is a versatile platform molecule to produce numerous important chemicals and materials, especially new-generation biocompatible and biodegradable poly(glycolic acid). In principle, it can be massively produced from syngas (CO + H2) via gas-phase hydrogenation of CO-derived dimethyl oxalate (DMO), but the groundbreaking catalyst represents a grand challenge. Here, we report the discovery of a Ni-foam-structured nanoporous Ni3P catalyst, evolutionarily transformed from a Ni2P/Ni-foam engineered from nano- to macro-scale, being capable of nearly fully converting DMO into MG at >95% selectivity and stable for at least 1000 h without any sign of deactivation. As revealed by kinetic experiments and theoretical calculations, in comparison with Ni2P, Ni3P achieves a higher surface electron density that is favorable for MG adsorption in a molecular manner rather than in a dissociative manner and has much higher activation energy for MG hydrogenation to ethylene glycol (EG), thereby markedly suppressing its overhydrogenation to EG.

Synthesis of methyl glycolate from the hydrogenation of dimethyl oxalate on Ag/SiO2 catalyst: the effects of Ag contents and promoters

A series of silica supported silver catalysts (Ag/SiO2) with Ag loading ranging from 5% to 15% were fabricated by the ammonia-evaporation deposition–precipitation method. The effect of Ag contents on the catalytic performance of the catalysts in the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was investigated. The result indicates that the catalyst with a 10 wt% silver loading exhibits the best catalytic activity and excellent long-term stability of more than 150 h. Characteristic studies by N2 adsorption, TPR, XRD, and XPS show that the Ag content has a significant impact on the physicochemical properties of the Ag/SiO2 catalyst. Furthermore, the influence of some additives (B, Ni, La, Ce, and Mo) on the catalytic performance of the most active 10%Ag/SiO2 catalyst in the DMO hydrogenation to MG was also studied.

Sonochemical synthesis of Zn-promoted porous MgO-supported lamellar Cu catalysts for selective hydrogenation of dimethyl oxalate to ethanol and their long-term stability

Zn-doped lamellar Cu nanocrystals supported on MgO NPs catalyst was developed and employed as novel and robust catalyst for the production of Ethanol from the environmentally benign hydrogenation reaction of dimethyl oxalate.

Plasma-enhanced copper dispersion and activity performance of Cu-Ni/ZrO2 catalyst for dimethyl oxalate hydrogenation

An efficient plasma-treated method of Cu-Ni/ZrO2 catalyst was prepared via the deposition–precipitation method for the selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). Compared with the untreated sample, the plasma- treated Cu-Ni/ZrO2 catalyst exhibited enhanced Cu dispersion and significantly improved selectivity to EG and stability for long time on stream. An ethylene glycol selectivity of higher than 95% was obtained after 150h of reaction. XRD and TEM measurements revealed that the mean copper particle size of the catalyst was remarkably reduced by plasma pretreatment. TPR and XPS measurements also indicated that copper dispersion was improved.

Synergistic Effect of a Boron-Doped Carbon-Nanotube-Supported Cu Catalyst for Selective Hydrogenation of Dimethyl Oxalate to Ethanol.

Heteroatom doping is a promising approach to improve the properties of carbon materials for customized applications. Herein, a series of Cu catalysts supported on boron-doped carbon nanotubes (Cu/xB-CNTs) were prepared for the hydrogenation of dimethyl oxalate (DMO) to ethanol. The structure and chemical properties of boron-doped catalysts were characterized by XRD, TEM, N2 O pulse adsorption, CO chemisorption, H2 temperature-programmed reduction, and NH3 temperature-programmed desorption, which revealed that doping boron into CNT supports improved the Cu dispersion, strengthened the interaction of Cu species with the CNT support, introduced more surface acid sites, and increased the surface area of Cu0 and especially Cu+ sites. Consequently, the catalytic activity and stability of the catalysts were greatly enhanced by boron doping. 100 % DMO conversion and 78.1 % ethanol selectivity could be achieved over the Cu/1B-CNTs catalyst, the ethanol selectivity of which was almost 1.7 times higher than that of the catalyst without boron doping. These results suggest that doping CNTs with boron is an efficient approach to improve the catalytic performance of CNT-based catalysts for hydrogenation of DMO. The boron-doped CNT-based catalyst with improved ethanol selectivity and catalytic stability will be helpful in the development of efficient Cu catalysts supported on non-silica materials for selective hydrogenation of DMO to ethanol.

Design of an Autoreduced Copper in Carbon Nanotube Catalyst to Realize the Precisely Selective Hydrogenation of Dimethyl Oxalate

AbstractAn autoreduced catalyst that comprised Cu nanoparticles encapsulated inside the nanochannels of carbon nanotubes (Cu@CNTs) was designed and prepared. As a result of the interaction of Cu species with the electron‐deficient interior surface of the CNTs, calcination could realize the autoreduction of copper oxide directly with CNTs as the reductant. In the hydrogenation of dimethyl oxalate (DMO), the autoreduced Cu@CNTs catalyst, which did not need to be prereduced, exhibited an excellent catalytic activity, high target product selectivity, and high catalytic efficiency. Furthermore, the effect of the calcination temperature on the autoreduction degree of Cu@CNTs and the product selectivity in DMO hydrogenation were investigated in detail. The results showed that the autoreduction degree could be tuned easily by changing the calcination temperature, and the highest selectivity of ethanol could be obtained over the catalyst calcined at 500 °C. The findings obtained will inspire the development of other autoreduced catalysts, the reduction degree and catalytic performance of which can be tuned as desired.