Hydrogenolysis Of Esters Research Articles

Ester hydrogenolysis via β-C-O bond cleavage catalysed by a phenanthroline-based PNNP-cobalt(I) complex.

A Co(I) catalyst bearing a phenanthroline-based PNNP ligand (2,9-bis((diphenylphosphanyl)methyl)-1,10-phenanthroline) exhibits long-range metal ligand cooperation behavior using a ligand backbone as a hydrogen reservoir and catalyses hydrogenolysis of benzyl benzoate derivatives via β-C-O cleavage with atmospheric pressure H2.

Study on the Hydrogenation of Ethyl Stearate to the Fatty Alcohol 1-Octadecanol over Ru on Tungstated Zirconia

Fatty alcohols are important products in the chemical industry, given that they are frequently used in the formulation of surfactants and lubricants. In this context, this work describes a catalytic heterogeneous approach for the production of 1-octadecanol (C18OH) from ethyl stearate (ES) using nanosized Ru-supported on tungstated zirconia (W/Zr). The activity and selectivity of this series of catalysts have been studied during the hydrogenation of ES in a batch reactor at 175 °C and PH2 = 40 bar. The so-prepared catalysts were characterized by a sort of characterization techniques (i.e., X-ray diffraction, H2-TPR, etc.), confirming the high dispersion and higher reducibility of Ru nanoparticles on the W/Zr surface (primarily tetragonal zirconia) with respect to pure zirconia. Overall, the catalysts were significantly active. In addition, a strong synergistic effect was revealed between Ru and W species, according to catalytic data. Finally, the reaction sequence towards fatty alcohol has also been elucidated, pointing to the ester hydrogenolysis to the aldehyde and ulterior hydrogenation of the latter as the main route for fatty alcohol formation.

Multifunctional WO3-ZrO2-Supported Platinum Catalyst for Remarkably Efficient Hydrogenolysis of Esters to Alkanes.

The hydrogenolysis of esters to alkanes is a key protocol for the synthesis of high-quality hydrocarbon fuels from renewable plant oils or fats. However, performing this process under mild energy-efficient conditions is challenging. Herein, we report a robust tungsten- and zirconium-oxide-supported platinum catalyst (Pt/WO3-ZrO2) for the hydrogenolysis of esters to alkanes at low temperatures (as low as 70 °C) and under ambient pressure (1 atm) of H2. For example, tristearin undergoes a complete conversion at 130 °C with more than 95% selectivity for the corresponding alkanes without carbon loss. In addition, the heterogeneous nature of the catalyst system reported herein permits multiple reuse of the catalyst without any significant loss of its high activity and selectivity. Mechanistic studies suggest that the multifunctional nature (acid and redox properties) of the WO3-ZrO2 support plays an important role in the high activity of the catalyst.

CuZnAl hydrotalcites as suitable precursors for chromium-free ester hydrogenolysis catalysts

Ester hydrogenolysis is industrially performed over Adkins catalysts. Their use is being restricted as they contain environmentally unfriendly Cr2O3. As a potential replacement, five co-precipitated CuZnAl catalysts with various Cu/Zn and Al/(Cu+Zn) atomic ratios were studied. The structure transformation during the whole catalyst lifecycle was determined. The catalyst precursors consisted of CuZnAl-hydrotalcite (HTC). Although the Cu/Zn ratio did not affect the HTC structure, an increase in Al content resulted in smaller Cu nanoparticles with a larger surface area. In the reduced catalysts, both Cu+ and Cu0 species were identified using FTIR-CO. XPS revealed catalyst surface reconstruction after catalyst reduction and catalytic reaction. The evaluation of the catalysts in dimethyl adipate hydrogenolysis indicated that the catalyst having the lowest Cu loading possessed the highest activity, due to its high SCu and Cu/Zn = 1. Generally, higher activity was achieved by reducing the Cu/Zn and increasing the Al/(Cu+Zn) ratios.

Enhanced activity of Cu/SiO2 and Cu/ZrO2 catalysts in dimethyl adipate hydrogenolysis

According to green chemistry principles, the process of ester hydrogenolysis is not sustainable. It is catalysed by Adkins CuCr2O3 catalyst that brings some environmental risks. Therefore, a design of new environmentally-friendly hydrogenolysis catalysts is highly desired. We investigated eight catalysts prepared using two methods - incipient wetness impregnation (IWI) and chemisorption-hydrolysis (CH) - with a combination of two types of supports - ZrO2 and two types of SiO2. The preparation method affects significantly the dispersion of the resulting copper phase in case of SiO2, and CH is essential to obtain very small and active Cu particles. On the other hand, when ZrO2 is used, the most critical aspect is its specific surface area, and a highly dispersed copper phase is formed on the high specific surface area sample, both for CH and IWI preparation methods.All eight prepared catalysts were investigated in dimethyl adipate hydrogenolysis to compare their activity and selectivity. Nice correlation between support – synthesis method – activity was found. ZrO2-based catalysts and CH resulted in more active catalysts compared to SiO2-based ones and IWI. Interestingly, Cu/SiO2 catalyst prepared by CH was more selective to the main reaction product hexane-1,6-diol due to the presence of acid sites. In this paper, the catalyst hydrogenolysis activity was increased twice, compared to our previous experiments using Cu/ZnO prepared by deposition-precipitation.

The importance of Brønsted acid sites on C[sbnd]O bond rupture selectivities during hydrogenation and hydrogenolysis of esters

Esters represent an important class of reagents and intermediates for the production of fine chemicals and polymers. In prior studies of homogeneous catalysis, molecular complexes have been reported to selectively cleave either carbonyl CO or acyl CO bonds of ester to ether or alcohols, respectively. In contrast, reactions of esters and H2 upon heterogeneous catalysts typically cleave acyl CO bonds and produce alcohols. Here, we demonstrate that the proximity of Brønsted acid sites to Pd nanoparticles and the thermodynamic strength of these Brønsted acid sites influence the rates and selectivities toward CO bond cleavage pathways either to ethers or alcohols during reactions of esters over bifunctional solid catalysts. The combined results from rate measurements as functions of H2 pressure, ester conversion, and methods to combine Pd nanoparticles and acidic supports; kinetic isotope effects; in situ Brønsted acid site titrations; and calorimetric assessments of Brønsted acid strength provide evidence for bifunctional pathways that require proximity between Brønsted acid sites and Pd atoms to form ethers. These findings suggest that Brønsted acid sites near Pd nanoparticles and with lower deprotonation energies promote the direct reduction of esters to ethers by cleaving the carbonyl CO bond. Taken together, these data indicate that direct reduction of esters to ethers involves the hydrogenation of the ester reactant to form hemiacetal at Pd nanoparticles, followed by dehydration of the hemiacetal at proximal acid sites, and subsequent hydrogenation of the enol ether. In comparison, hydrogenolysis of acyl CO bonds of the ester reactant involves the reaction of a hydrogenated intermediate (plausibly hemiacetal) upon Pd nanoparticles to form the corresponding alcohol and aldehyde products. Among the materials examined, Pd nanoparticles supported on WO3 catalyze the direct reduction of esters and lactones to corresponding ethers and remain stable over extended periods of time on stream (∼42 h). These findings offer a foundation for further design and improvement of heterogeneous catalysts for the selective reduction of esters and other challenging hydrogenations.

Understanding of the Key Factors Determining the Activity and Selectivity of CuZn Catalysts in Hydrogenolysis of Alkyl Esters to Alcohols

CuZn catalysts are perspective catalysts for esters hydrogenolysis, but more knowledge is needed to optimize their catalytic performance. In this work, we consider the impact of CuZn catalysts composition on their structure, activity, selectivity, and stability in esters hydrogenolysis. Four catalysts with various Cu/Zn ratio were synthesized by a co-precipitation and characterized in as-prepared, calcined, reduced, and spent state by XRF, XRD, N2 physisorption, CO2-TPD, NH3-TPD, and N2O chemisorption. XRD data revealed the effect of the composition on the size of Cu and ZnO particles. The catalytic performance was investigated using an autoclave. All catalysts exhibited high methyl hexanoate conversion about 48–60% after 3 h but their activity and selectivity were found to be dependent on Cu/Zn ratio. The conversion of methyl hexanoate and hexyl hexanoate was compared to explain the observed product selectivity. Moreover, the catalysts stability was investigated in three consecutive reaction cycles and correlated with changes in the size of constituent particles. Moreover, when different esters were tested, a slight decrease in conversion and increase in alcohol selectivity with a growth in molecule size was observed. Obtained results allow making a conclusion about the optimal composition that provides the good performance of CuZn catalysts in ester hydrogenolysis.

Understanding of the key properties of supported Cu-based catalysts and their influence on ester hydrogenolysis

The application of Cr-free Cu-based catalysts in ester hydrogenolysis is a modern environmentally-friendly research approach. The comprehensive study of four supported Cu-based catalysts was performed using 8 wt% of Cu loaded on Al2O3, ZnO, TiO2 and ZrO2 supports by an impregnation method. Using XRD, H2-TPR, BET, pyridine-TPD, CO2-TPD and N2O-RFC methods, the effect of the support on the formation of Cu-nanoparticles was described. Al2O3 was evaluated as the support ensuring the highest nanoparticles dispersion, while Cu nanoparticles in Cu-TiO2 were liable to sintering. The catalysts were tested in dimethyl adipate hydrogenolysis, where the catalyst performance and activity (TOF) were evaluated and Cu-ZrO2 showed the best results. A correlation between the number of acid-base sites and the catalyst selectivity was revealed and the catalyst effect on the formation of various by-products was described. The intrinsic selectivity to hydrogenolysis products was found to decrease with the increasing acid-base character of the supports whereas the selectivity to transesterification and cyclization products increased. The hydrogenolysis activity was not a simple function of the number of the surface copper atoms, but it was affected by the support nature and its properties.

Critical evaluation of parameters affecting Cu nanoparticles formation and their activity in dimethyl adipate hydrogenolysis

Supported copper catalysts are promising alternative to replace CuCr catalysts in ester hydrogenolysis and decrease the environmental footprint of the process. However, the effect of the support properties on the Cu nanoparticles formation and, consequently, on the final hydrogenolysis performance has not been investigated in detail. Therefore, we have selected 10 supports with different textural-structural properties and impregnated them by incipient wetness impregnation to achieve 8 wt% Cu loading. Although the silica-based supports provided much larger surface area to deposit Cu compared to ZnO, MgO, or TiO2, the final Cu dispersion was similar for these catalysts due to the insufficient electrostatic attraction. A significant improvement was observed when using ZrO2 as a support, while the best Cu dispersion was achieved using alumina-based supports. The reduced catalysts were tested in dimethyl adipate (DMA) hydrogenolysis to obtain hexane-1,6-diol (HDOL). Due to the good Cu dispersion ensured by ZrO2 and alumina supports, they outperformed the rest of the catalysts reaching the highest DMA conversion of 36 and 22–25%, respectively. Moreover, Cu-ZrO2 reached the highest hydrogenolysis activity (TOFH) due to a good copper-zirconia interaction. The maximum HDOL selectivity of about 8% was obtained over alumina-based catalysts. The increasing number of acid-base sites was found to be responsible for decreasing HDOL selectivity. Over these sites, a large amount of transesterification by-products (<80%) and other side products were formed. Although the larger support surface area may ensure a better Cu dispersion, the acid-base sites or electrostatic attraction during impregnation play a key role by affecting the Cu nanoparticle formation and, consequently, the final catalyst performance.

Towards efficient Cu/ZnO catalysts for ester hydrogenolysis: The role of synthesis method

Cu/ZnO catalysts represent an environmentally friendly alternative to Adkins catalysts used for ester hydrogenolysis. Cu/ZnO are mostly synthesized by co-precipitation (COP); however, other synthesis methods may help to obtain small highly dispersed Cu crystallites advantageous for catalyst activity. A comparative study on the effect of synthesis method on Cu/ZnO catalysts properties and activity is missing. Thus, we synthesized 8 wt% Cu/ZnO catalysts by five methods (COP, deposition-precipitation (DP), chemisorption-hydrolysis (CH), incipient wetness (IWI) and wet impregnation (WI)), characterized and tested them in dimethyl adipate hydrogenolysis. The CH-prepared catalyst was prone to Cu sintering, which impaired its performance. IWI led to large Cu nanoparticles, pore blocking and poor catalytic performance. COP and DP resulted in the smallest Cu nanoparticles (13−14 nm), largest Cu surface area (3.9–4.2 m2 gcat−1) and specific surface area (40−43 m2 gcat−1) reflected in their superior catalytic activity making DP a good alternative to COP to prepare active Cu/ZnO catalysts.

Do metal-oxide promoters of Cu hydrogenolysis catalysts affect the Cu intrinsic activity?

The well-established ester hydrogenolysis process has to be further improved to reduce its high energy demand and to replace used Adkins CuCr catalysts by chromium-free alternatives. In this study, the copper-based catalyst was modified by ZnO, ZnO with Al2O3 or MgO to elucidate the metal-oxide influence on catalyst structure, activity, performance and stability in ester hydrogenolysis. The catalysts composition, structure and physicochemical properties were examined by AAS, XRD, TPR, BET, N2O-RFC, TGA-MS, NH3-TPD and CO2-TPD. It was confirmed that copper itself possesses high intrinsic activity for ester hydrogenolysis but the unpromoted copper species were very unstable. All used metal oxides were proven to be structural promoters stabilizing copper species and increasing the number of active sites. Consequently, they enhanced remarkably catalyst performance in dimethyl adipate conversion despite the decreased intrinsic activity of Cu active sites. All prepared catalysts outperformed a commercial CuCr catalyst in dimethyl adipate hydrogenolysis.

Solvent-free hydrodeoxygenation of bio-lipids into renewable alkanes over NiW bimetallic catalyst under mild conditions

Solvent-free hydrodeoxygenation (HDO) of bio-lipids into renewable alkanes by non-precious Ni metal catalysts usually required harsh reaction conditions of, for example, over 360 °C. Herein, we reported a NiW bimetallic catalyst that reached a 100 % HDO efficiency over oleic acid under a mild condition of 320 °C. This was due to a catalytic synergy of Ni and oxygen vacancy (OV) site over the rate-determined step, C36 ester hydrogenolysis, in HDO. The OV site created by a partially H2 reduction of WO3 was confirmed by XPS and UV–vis characterizations. Primary density functional theory calculation demonstrated that OV had stronger adsorption over carbonyl oxygen atom in carboxyl group compared to Ni site. In this way, the activation and cleavage of CalkoxyO bond during C36 ester hydrogenolysis under mild conditions were realized. This developed NiW bimetallic catalyst highlighted a great promise for the solvent-free HDO of bio-lipids into renewable alkanes under mild conditions.

CuZn Catalysts Superior to Adkins Catalysts for Dimethyl Adipate Hydrogenolysis

AbstractIndustrial hydrogenolysis of esters to alcohols relies on the use of Adkins catalysts whose production and disposal is an environmental burden. This work is focused on CuZn catalysts that represent an ecological alternative to Adkins catalysts. Four CuZn catalysts with Cu/Zn atomic ratio ranging from 0.5 to 2.0 and single phase CuO and ZnO catalysts were prepared by co‐precipitation and their hydrogenolysis activity was compared with a commercial Adkins catalyst. Dimethyl adipate was used to test the catalyst performance in a flow reactor at temperatures ranging from 175 to 205 °C and hydrogen pressure of 16 MPa. The increase in ZnO content was directly responsible for the reduction in copper crystallite size and increase in the catalyst specific surface area. The CuZn catalysts exhibited higher conversion than the Adkins catalyst despite their specific surface area declined during the experiments more significantly than that of the Adkins catalyst. Nonetheless, the TOF of CuZn catalysts exceeded that of the commercial Adkins catalyst.

Hydrogenolysis of Amide Acetals and Iminium Esters

AbstractAmide acetals and iminium esters were hydrogenated into amines under very mild reaction conditions over common hydrogenation catalysts. This finding provides a new strategy for the selective reduction of amides. The synthetic utility of this approach was demonstrated by the selective reduction of amides bearing ester and nitrile groups.

A general approach for the synthesis of bimetallic M–Sn (M = Ru, Rh and Ir) catalysts for efficient hydrogenolysis of ester

A versatile synthetic method was applied for the preparation of Sn containing bimetallic catalysts.

Catalysts for Fatty Alcohol Production from Renewable Resources

AbstractFatty alcohols may be produced through the processing of fatty acids or their esters derived from palm or coconut oils. Fatty alcohol technology can be classified into two categories (a) a slurry‐phase process in which the fatty acid or its ester is converted into alcohol using a powdered catalyst and (b) fixed bed technology in which the fatty acid or its ester is processed over a formed catalyst, e.g. tablets or extrudates. Historically copper‐based catalysts are employed for achieving ester hydrogenolysis. In recent years, studies were also focused on precious metal catalysts for this process. This paper will critically review existing literature pertaining to the catalysts that operate at diverse conditions, handle different feedstocks, and are compatible with a variety of unit operations used by the fatty alcohol manufacturers. There is an effort to develop environmentally friendly non‐chrome copper catalyst in this process. Some recent progress on bimetallic Cu‐Fe catalyst and understanding Cu‐Fe interaction has been reported. Current development on homogenous catalysts in this process was carefully reviewed. The catalyst deactivation mechanism has been investigated and effect of different impurities, mainly phosphorous, sulfur, chloride, water, glycerine and free fatty acid was thoroughly reviewed.

Ethyl formate hydrogenolysis over Mo2C-based catalysts: Towards low temperature CO and CO2 hydrogenation to methanol

Ester hydrogenolysis is a key step in the production of alcohols and new catalysts are being sought to improve the performance and sustainability of this process. Research described in this paper investigated the use of Cu, Mo2C, and Mo2N-based catalysts for the hydrogenolysis of ethyl formate at 105–150°C and 30bar H2. The high surface area Mo2C-based catalysts were more active and selective to methanol than the Mo2N-based catalysts. The deposition of nanoscale Cu and/or Pd particles onto the Mo2C or Mo2N resulted in significant enhancements in the methanol selectivities. The methanol selectivities varied with the acidity or basicity of the support suggesting some degree of cooperation between the Cu or Pd particles and the support. Temporal variations in rates for the Cu/Mo2C catalyst were consistent with first order kinetics with regard to ethyl formate and the activation energy was 44kJ/mol. The best performance was achieved over a Pd-Cu/Mo2C catalyst; this material outperformed, by a significant margin, the oxide supported Cu catalysts. Given their high activities and selectivities, the Mo2C supported catalysts are attractive candidates for ester hydrogenolysis, including the intermediate step during the low temperature, cascade hydrogenation of CO and CO2 to methanol.

Unique Chemoselective Hydrogenation using a Palladium Catalyst Immobilized on Ceramic

AbstractA heterogeneous palladium catalyst supported on a ceramic (5 % Pd/ceramic) was developed. The catalyst exhibited a specific chemoselectivity for hydrogenation that has never been achieved by other palladium‐catalyzed methods. Either aliphatic or aromatic N‐Cbz groups could be deprotected to the corresponding free‐amines, while the hydrogenolysis of benzyl esters and ethers did not proceed. Furthermore, aryl chlorides and epoxides were tolerant under the Pd/ceramic‐catalyzed hydrogenation conditions. 5 % Pd/ceramic could be reused without any loss of catalyst activity, as no palladium leaching was detected in the reaction media.

Chemoselective Hydrogenation Catalyzed by Pd on Spherical Carbon

AbstractWe have developed a highly chemoselective hydrogenation method using a novel palladium catalyst supported on spherical carbon (0.5 % Pd/SC). The 0.5 % Pd/SC exhibited a novel catalytic activity and could achieve the chemoselective hydrogenation of alkynes, alkenes, azides, nitro groups, and aliphatic O‐tert‐butyldimethylsilyl (TBS) ethers without hydrogenolysis of benzyl esters, benzyl ethers, nitriles, aromatic ketones, N‐carbobenzyloxy (N‐Cbz) protective groups, and aromatic O‐TBS ethers.

Influence of reaction conditions on one-step hydrotreatment of lipids in the production of iso-alkanes over Pt/SAPO-11

A one-step hydrotreatment of soybean oil to produce iso-alkanes has been carried out over a Pt/SAPO-11 catalyst in a fixed-bed reactor. The influence of reaction conditions such as temperature, pressure, hydrogen/oil ratio, and space velocity on the catalytic performance has been investigated. From the levels of intermediate products, gas products (CO, CO2) and the target product (alkane), it was found that the hydrogenolysis of esters, fatty acids and fatty aldehydes and the formation of fatty alcohols were prohibited, which led to high selectivity for hydrodecarboxylation and hydrodecarbonylation at high temperature, low pressure or low hydrogen/oil ratio. The selectivity of the isomerization increased when temperature increased or space velocity decreased, while pressure and hydrogen/oil ratio were found to have no influence. A plausible reaction pathway has been proposed based on these results.