Glycerol Hydrogenolysis Reaction Research Articles

Ir-Fe bimetallic catalysts for selective glycerol hydrogenolysis

This work studied the effect of adding Fe to an Ir/γ-Al2O3 catalyst in different Fe/Ir molar ratios (0.5, 1.0, and 2.0) on the conversion and selectivity of the glycerol hydrogenolysis reaction. Additionally, the effect of the calcination of the solids was evaluated. The catalysts were prepared by incipient wetness impregnation of the Ir and Fe salts on the support and were characterized by textural analysis, XRD, TPR, XPS, and TEM-EDS techniques. The interaction between Ir and Fe was evidenced in the characterization of the catalysts. The addition of Fe to the Ir catalyst led to an increase in activity; however, this effect was better observed for the non-calcined catalyst series. The calcined catalyst series did not present a significant increase in glycerol conversion and selectivity to 1,2-PDO, probably due to the sintering of Ir occasioned by the catalyst's calcination, as observed in the characterization. For non-calcined bimetallic catalysts, the conversion increased from 7 % to 21.5 % for IrFe2.0/γ-Al2O3 catalyst, probably due to the synergic effect between both metals and the formation of Ir-Fe bimetallic particles, as evidenced in EDS mapping and XPS analysis. In the presence of this catalyst, selectivity to 1,2-PDO remained high (90.1 %).

Crude Glycerol Hydrogenolysis to Bio-Propylene Glycol: Effect of Its Impurities on Activity, Selectivity and Stability

The wide availability of crude glycerol and its low market price make this by-product of the biodiesel industry a promising raw material for obtaining high-value-added products through catalytic conversion processes. This work studied the effect of the composition of different industrial crude glycerol samples on the catalytic hydrogenolysis to 1,2-propylene glycol. A nickel catalyst supported on a silica–carbon composite was employed with this purpose. This catalyst proved to be active, selective to 1,2-propylene glycol and stable in the glycerol hydrogenolysis reaction in the liquid phase when analytical glycerol (99% purity) was employed. In order to determine the effect of crude glycerol composition on the activity, selectivity and stability of this catalyst, industrial crude glycerol samples were characterized by identifying and quantifying the impurities present in them (methanol, NaOH, NaCl and NaCOOH). Reaction tests were carried out with aqueous solutions of analytical glycerol, adding different impurities one by one in their respective concentration range. These results allowed for calculating activity factors starting from the ratio between the rate of glycerol consumption in the presence and in the absence of impurities. Finally, catalyst performance was evaluated employing the industrial crude glycerol samples, and a kinetic model based on the power law was proposed, which fitted the experimental results taking into account the effect of glycerol impurities. The fit allowed for predicting conversion values with an average error below 8%.

A multi-functional Ru Mo bimetallic catalyst for ultra-efficient C3 alcohols production from liquid phase hydrogenolysis of glycerol

Ru and Mo bimetallic catalysts supported on active carbon modified by phosphotungstic acid (PW) were designed and applied in glycerol hydrogenolysis reaction. The physicochemical properties of the catalysts were characterized and the presence of active sites was investigated from the perspective of the glycerol hydrogenolysis performance. The MoO x is highly selective for the C—O bond cleavage of glycerol molecules, which can reasonably regulate the strong C—C bond cleavage activity of Ru nanoparticles. By using sequential deposition of Ru and Mo supported on mesoporous PW-C, the characterization results show that the combination of isolated low-valence MoO x with metal Ru particles can form “MoO x -Ru-PW”, which provides highly catalytic activity toward C—O bond cleavage, selectively producing more C3 alcohols (mainly 1,2(3)-propanediol). The glycerol conversion of 1% Mo/Ru/PW-C catalyst was 59.6%, the selectivity of C3 alcohol was 96.1%, and the selectivity of propanediol (1,2(3)-propanediol) was 94.9%. It is noteworthy that the selectivity of 1,3-propanediol reached 20.7% when the PW was 21.07% (mass). This study provides experimental evidence for the tandem dehydration and hydrogenation mechanism of the multifunctional Mo/Ru/PW-C catalyst.

Study of the Glycerol Hydrogenolysis Reaction on Cu, Cu-Zn, and Cu-ZnO Clusters.

Quantum chemistry calculations have been performed to access the efficacy of Cu-based catalysts in various mechanistic steps of the glycerol hydrogenolysis reaction. Calculations are first performed for reactants in the gas phase (noncatalyzed system) and reactants in the gas phase with a 3-atom Cu cluster (catalyzed system). We demonstrate that the glycerol to ethylene glycol conversion is preferred in the noncatalyzed system but glycerol conversion to 1,2-propanediol via the 2-acetol intermediate is preferred in the catalyzed system. We next analyze the adsorption energies of the reactant and product species involved in the glycerol to 1,2-PDO reaction on an 8-atom Cu cluster and Cu cluster doped with a Zn atom or a ZnO molecule. Finally, we study the effects of Zn or ZnO doping on the activation barriers of the two steps of the glycerol to 1,2-PDO reaction.

Promotional effect of transition metals (Cu, Ni, Co, Fe, Zn)–supported on dolomite for hydrogenolysis of glycerol into 1,2-propanediol

Hydrogenolysis of biomass-derived glycerol is an alternative route to produce 1,2-propanediol. A series of transition metals supported on dolomite catalysts (Cu/Dol, Ni/Dol, Co/Dol, Fe/Dol, Zn/Dol) were prepared via impregnation, calcined at 500 °C and reduced at 600 °C. The synthesized catalysts were then characterized by BET, BJH, XRD, H2-TPR, NH3–TPD, and SEM, and subsequently evaluated in glycerol hydrogenolysis reaction to produce 1,2-propanediol (1,2-PDO). The nature of transition metals was found to influence the activation of the catalysts. Among the tested catalysts, copper supported on dolomite (Cu/Dol) exhibited appreciable hydrogenolysis performance due to the mutual interaction between the copper species and the dolomite. The findings from the various characterization results showed the addition of copper to dolomite ameliorates the chemical and reduction of the catalyst. It appears that the copper species were essentially enriched on the grain surfaces of the dolomite, the reduction properties, and the acidity of the catalyst enhanced. All the features of Cu/Dol catalyst contributed to the high glycerol conversion (78.5%) and high 1,2-PDO selectivity (79%) with low methanol production as the by-product at 200 °C of reaction temperature, 4 MPa of reaction pressure and 10 h of reaction time.

Experimental and computational study on roles of WOx promoting strong metal support promoter interaction in Pt catalysts during glycerol hydrogenolysis

Biodiesel is of high interest due to increased demand for energy with the concern regarding more sustainable production processes. However, an inevitable by-product is glycerol. Hence, the conversion of this by-product to higher-value chemicals, especially 1,3-propanediol (1,3-PDO) via glycerol hydrogenolysis reaction, is one of the most effective pathways towards a profitable process. In general, this process is catalyzed by a highly active Pt-based catalyst supported on γ-Al2O3. However, its low 1,3-PDO selectivity and stability due to surface deactivation of such catalysts remained. This led to the surface modification by WOx to improve both the selectivity by means of the increased Brønsted acidity and the stability in terms of Pt leaching-resistance. Hence, we applied experimental and density functional theory (DFT)-based techniques to study the fundamentals of how WOx modified the catalytic performance in the Pt/γ-Al2O3 catalyst and provided design guidelines. The effects of WOx promoter on improved activity were due to the shifting of the total density of states towards the antibonding region evident by the total density of states (TDOS) profile. On the improved 1,3-PDO selectivity, the main reason was the increasing number of Brønsted acid sites due to the added WOx promoter. Interestingly, the stability improvement was due to the strong metal-support interaction (SMSI) that occurred in the catalyst, like typical high leaching-resistant catalysts. Also, the observed strong metal-support-promoter interaction (SMSPI) is an additional effect preventing leaching. The SMSPI stemmed from additional bonding between the WOx species and the Pt active site, which significantly strengthened Pt adsorption to support and a high electron transfer from both Pt and Al2O3 to WOx promoter. This suggested that the promising promoter for our reaction performed in the liquid phase would improve the stability if SMSI occurred, where the special case of the WOx promoter would even highly improve the stability through SMSPI. Nevertheless, various promoters that can promote SMSPI need investigations.

Understanding the deactivation behavior of Pt/WO3/Al2O3 catalyst in the glycerol hydrogenolysis reaction

The selective hydrogenolysis of glycerol to 1,3-propanediol is a highly important reaction for both improving the profitability of biodiesel and valorization of biomass. While intensive research efforts have been devoted to enhancing the catalytic activity and selectivity, little is focused on the stability although the latter is of paramount importance to practical applications. In this work, we investigated the stability of Pt/WO3/Al2O3 and observed a continuous deactivation trend during a 700 h time-on-stream run. Neither the leaching of active W nor the coking was responsible for the deactivation. Instead, XRD, HAADF-STEM and CO chemisorption results clearly showed the occurrence of significant aggregation of Pt particles, which caused a remarkable decrease of Pt-WOx interfacial sites. As a consequence, strong Brönsted acid sites which were in situ formed by H2 dissociation at the Pt-WOx interfacial sites were reduced, leading to the deactivation of the catalyst.

Improving Selectivity to 1,3-Propanediol for Glycerol Hydrogenolysis Using W- and Al-Incorporated SBA-15 as Support for Pt Nanoparticles

Tungsten and aluminum were directly incorporated into SBA-15 via one-step synthesis method under an acidic medium. The W- and Al-incorporated SBA-15 was applied as support for Pt nanoparticles to catalyze glycerol hydrogenolysis toward 1,3-propanediol. A combination of the characterization techniques showed that the tungsten and aluminum were incorporated into SBA-15 homogeneously, and the platinum nanoparticles could be uniformly dispersed on the modified-SBA-15. The catalytic performance of Pt-loaded SBA-15 could be significantly improved after the incorporation of tungsten and aluminum into SBA-15, reaching a 1,3-PDO selectivity near 50% when the glycerol conversion was 66%. The glycerol hydrogenolysis reaction proceeds through a dehydration–hydrogenation process, and the enhanced 1,3-PDO selectivity greatly benefited from the synergism between Bronsted acid and Lewis acid sites, which is tightly related with the incorporation of tungsten and aluminum species on the modified SBA-15.

Toward the Sustainable Synthesis of Propanols from Renewable Glycerol over MoO3-Al2O3 Supported Palladium Catalysts

The catalytic conversion of glycerol to value-added propanols is a promising synthetic route that holds the potential to overcome the glycerol oversupply from the biodiesel industry. In this study, selective hydrogenolysis of 10 wt% aqueous bio-glycerol to 1-propanol and 2-propanol was performed in the vapor phase, fixed-bed reactor by using environmentally friendly bifunctional Pd/MoO3-Al2O3 catalysts prepared by wetness impregnation method. The physicochemical properties of these catalysts were derived from various techniques such as X-ray diffraction, NH3-temperature programmed desorption, scanning electron microscopy, 27Al NMR spectroscopy, surface area analysis, and thermogravimetric analysis. The catalytic activity results depicted that a high catalytic activity (>80%) with very high selectivity (>90%) to 1-propanol and 2-propanol was obtained over all the catalysts evaluated in a continuously fed, fixed-bed reactor. However, among all others, 2 wt% Pd/MoO3-Al2O3 catalyst was the most active and selective to propanols. The synergic interaction between the palladium and MoO3 on Al2O3 support and high strength weak to moderate acid sites of the catalyst were solely responsible for the high catalytic activity. The maximum glycerol conversion of 88.4% with 91.3% selectivity to propanols was achieved at an optimum reaction condition of 210 ∘ C and 1 bar pressure after 3 h of glycerol hydrogenolysis reaction.

Effect of Silica Particle Size on Texture, Structure, and Catalytic Performance of Cu/SiO2 Catalysts for Glycerol Hydrogenolysis

The influences of carrier particle sizes of Cu/SiO2 catalysts for hydrogenolysis of glycerol were studied use mono-dispersed silica as models. Catalysts were prepared by precipitation method with the average size of the mono-dispersed silica supports varying of 10, 20, and 90 nm. Characterization of the catalysts show that the physical properties such as pore volume and BET surface area of the catalysts were largely affected by the carrier particle size of silica. However, the copper dispersion of the three samples were similar. XPS patterns show a difference in the chemical states of copper species, small carrier particle size induced formation of copper phyllosilicate, which benefits on the stability of copper species in reaction. The overall activity in the reaction of glycerol hydrogenolysis shows a correlation with the carrier particle size. The small carrier particles prevent the copper species from aggregation thus such catalysts exhibit good catalytic activity and stability.

Combination of DOSY and 1D selective gradient TOCSY: Versatile NMR tools for identify the mixtures from glycerol hydrogenolysis reaction

Hydrogenolysis is necessary for preparing various value-added chemicals from glycerol. Routine methods like GC and HPLC are not sufficient for analysis the reaction mixtures because the products usually have high boiling or similar polarity, especially when new chromatographic peaks are found which requires other technologies such as NMR. Although they were developed for years, but either DOSY or 1D selective TOCSY NMR has nature limitations. Herein we took their advantages and combined them to analyse glycerol hydrogenolysis mixtures for the first time. A model reaction mixture was first pseudo separated in DOSY spectrum, and 1D selective gradient TOCSY was further applied to assign the overlapped signal which could not be confirmed just by DOSY. A genuine reaction mixture was tried afterwards, and main signals could be assigned well in DOSY diffusion dimension. Notably, n-propanol was found as by-product by 1D selective gradient TOCSY, which is not visible in DOSY spectrum. The experimental results demonstrate that the combination of these two NMR methods could provide a fast, effective, feasible and reliable way for the identification of glycerol hydrogenolysis mixtures and is expected to apply in other research areas.

Influence of the Support of Bimetallic Platinum Tungstate Catalysts on 1,3‐Propanediol Formation from Glycerol

AbstractThree aluminium oxide materials and a HZSM‐5 zeolite were used as supports of bimetallic Pt‐WOx catalysts to establish structure–activity relationships in the glycerol hydrogenolysis reaction. The surface W density and the intimate contact between Pt and WOx were key parameters. Surface W density controls the formation of polytungstates, the only species able to produce the weak Brønsted acidity that is required to produce 1,3‐propanediol selectively. The comparison between the HZSM‐5 and the Al2O3 supports demonstrated that an increment of the medium Brønsted acidity is detrimental for the selective 1,3‐propanediol formation as it promotes reactions that yield 1‐propanol and propane. An increase of the dispersion of Pt on the Pt/WOx/Al2O3 catalysts led to higher glycerol conversions but also promoted the hydrogenolysis routes that lead to 1,2‐ and 1,3‐propanediol similarly. On the contrary, an increase of the Pt metal content favoured the hydrogenolysis route that leads to 1,3‐propanediol significantly. A more intimate contact between Pt and WOx promoted the hydrogenation of the intermediate carbocation, formed and stabilised on a polytungstate active site, into 1,3‐propanediol.

Hydrogenolysis of Glycerol over γ-Al2O3-Supported Iridium Catalyst

In recent years, much attention has been focused on the hydrogenolysis of biodiesel derived glycerol to other high value products for the sustainable development and efficient valorization strategies. In the present work, alumina-supported Ir catalyst was prepared by the incipient wetness impregnation method and tested in the glycerol hydrogenolysis reaction. The synthesized catalyst was characterized by neutron activation analysis, N2 physisorption, and H2 chemisorption techniques. The experiments standard conditions were 150 mL feed volume, 0.3 g catalyst, 1500 rpm stirring speed, and 5 wt% glycerol aqueous solution for 4 h. The effects of catalyst amount, temperature, hydrogen pressure, stirring speed, and solution pH on glycerol conversion and selectivity of the principal products obtained were also investigated. The glycerol conversion and the 1,2-propanediol selectivity varied from 4.9% to 22% and from 23.8% to 70.3%, respectively. It was found that the selectivity of 1,2-propanediol increased significantly with the increased alkalinity of the reaction medium.

Deactivation of CuZn Catalysts Used in Glycerol Hydrogenolysis to Obtain 1,2-Propanediol

Different CuZn catalysts were prepared by coprecipitation method with Cu/Zn atomic ratio of 0.2, 0.4, 1.0, 2.5 and 6.0. Monometallic Zn and Cu catalysts and a bimetallic catalyst (Cu/Zn = 2.5) prepared by physical mixture of the precursors were also studied. These catalysts were tested in the glycerol hydrogenolysis reaction and the higher yields to 1,2-propanediol were achieved for Cu/Zn atomic ratio ≥ 1 samples. The deactivation of a representative catalyst (Cu/Zn = 1) was evaluated and its yield to 1,2 propanediol decreases until ca 40% after five runs. To explain this behavior, fresh and used catalysts were characterized by different techniques. Chemical analysis of solid catalysts and liquid reaction medium confirmed the leaching of Zn species under our reaction conditions. This process promotes Cu sintering which is proposed as the actual reason of the observed deactivation in the glycerol hydrogenolysis for this catalytic system.

Bio-propylene glycol by liquid phase hydrogenolysis of glycerol with Ni/SiO2-C catalysts

The development of catalytic materials, hydrothermally stable and selective to the desired products, is still a challenge. The aim of the present work is to prepare a nickel catalyst with a metal loading of 5wt% Ni supported on a SiO2-C composite, to be used in the liquid-phase glycerol hydrogenolysis reaction. The most active and selective catalyst to 1,2-propylene glycol (1,2-PG) was Ni/SC-095, which presented surface acidity fundamentally represented by the presence of carboxylic groups which promoted the CO cleavage reactions of the glycerol primary carbon to produce acetol, and subsequently by hydrogenation to produce 1,2-PG.Concerning the selection of operating conditions, the influence of the most relevant variables of the process were analyzed, i.e., temperature (220–260°C), glycerol concentration (30–65%), and hydrogen partial pressure (0–4MPa). The best result was obtained at 260°C with 30wt% glycerol, 6h on reaction and a hydrogen partial pressure of 2MPa. Under these conditions, selectivities of 77% towards 1,2-PG and 3% to acetol were obtained, with 56% of conversion.It was demonstrated that there are no important structural changes through the characterization of the used samples. Both the SC-095 support and the Ni/SC-095 catalyst maintained their BET surface area. By XRD and TEM, there could be a slight increase in particle size, which would indicate good resistance to sintering against the severe hydrothermal conditions of this reaction.

Selective hydrogenolysis of glycerol to propylene glycol in a continuous flow trickle bed reactor using copper chromite and Cu/Al2O3 catalysts

The glycerol hydrogenolysis reaction was performed in a continuous flow trickle bed reactor using a water glycerol feed and both copper chromite and Cu/Al2O3 catalysts. The commercial copper chromite had a higher activity than the laboratory prepared Cu/Al2O3 and was used for most of the tests. Propylene glycol was the main product with both catalysts, acetol being the main by-product. It was found that temperature is the main variable influencing the conversion of glycerol. When the state of the glycerol-water reactant mixture was completely liquid, at temperatures lower than 190 oC, conversion was low and deactivation was observed. At reaction temperatures of 210-230 oC the conversion of glycerol was complete and the selectivity to propylene glycol was stable at about 60-80% all throughout the reaction time span of 10 h, regardless of the hydrogen pressure level (1 to 20 atm). These optimal values could not be improved significantly by using other different reaction conditions or increasing the catalyst acidity. At higher temperatures (245-250 oC) the conversion was also 100%. Under reaction conditions at which copper chromite suffered deactivation, light by-products and surface deposits were formed. The deposits could be completely burned at 250 oC and the catalyst activity fully recovered.

Selective hydrogenolysis of glycerol over Ir-Ni bimetallic catalysts

The effect of the addition of Ni to Ir/γ-Al2O3 was studied for glycerol hydrogenolysis reaction. The catalysts were characterized by textural analysis, XRD, H2-TPR, XPS and TEM. In all cases, the addition of Ni to Ir/γ-Al2O3 produced a significant increase in glycerol conversion, and a high selectivity to 1,2-PDO was maintained. TOF values increased from 0.4×10−2s−1 for Ir monometallic catalyst, to 4.3×10−2s−1 for bimetallic IrNi2_C catalyst. The latter was the most active catalyst among the calcined bimetallic catalysts. Selectivity to 1,2-PDO had an insignificant decrease from 89.9% for Ir monometallic catalyst to 83.1% for IrNi2_C catalyst. However, non-calcined IrNi2 catalyst presented a TOF value of 1.3×10−2s−1. This result indicates that the calcination step was fundamental to obtain a strong Ir-Ni interaction that lead to better performances of the bimetallic catalysts. Ir-Ni interaction was evidenced by XPS analyses of the calcined series of catalysts, where the presence of an Irδ+ species was observed (0<δ<4), suggesting an electronic density transferring from Ni to Ir.

Preparation of Al2O3/AlF3-Supported Ruthenium Catalysts for the Hydrogenolysis of Biodiesel-Derived Crude Glycerol

Hydrogenolysis of biodiesel-derived glycerol to value-added chemicals has emerged as an innovative approach to biowaste valorization for a more sustainable society. In the present work, Ru catalysts on Al2O3/AlF3 supports with different AlF3 content were prepared by the aqueous incipient wetness method and tested in the reaction of glycerol hydrogenolysis for the first time. The prepared catalysts were characterized by neutron activation analysis, N2 physisorption, and H2 chemisorption techniques. The catalytic hydrogenation of crude glycerol was performed at a temperature of 473 K and a hydrogen pressure of 4.0 MPa, using a 5 wt % glycerol aqueous solution for 4 h with comprehensive characterization of liquid- and gas-phase products. Texture, structure, and activity of the prepared catalysts were significantly affected by the fluoridation. To understand the mechanism of possible reactions for glycerol hydrogenolysis better, the effects of pH and individual hydrogenolysis of most of the products of the glycerol reaction were investigated.

Influence of Pd precursors and Cl addition on performance of Pd-Re catalysts in glycerol hydrogenolysis to propanediols

Pd-Re/SBA-15 catalysts with different Pd precursors were prepared by the impregnation method. N2 adsorption-desorption, XRD, H2-TPR, TEM and NH3-TPD were used to characterize the physical and chemical properties of the catalysts. Pd-Re catalysts with different precursors showed different activities in the reaction of glycerol hydrogenolysis. 5Pd-5Re/SBA-15 with PdCl2 as Pd precursor had higher activity than those with Pd(NO3)2 and Pd(OAc)2 as precursors. The existence of Cl could affect the particle sizes, reduction behaviors and the acid properties of Pd-Re catalysts.

Support effect on the bimetallic structure of Ir–Re catalysts and their performances in glycerol hydrogenolysis

Comparative study was made between the bimetallic Ir–Re catalyst supported on amorphous silica-alumina (ASA) and the ones supported on de-aluminated ASA (D-ASA) to elucidate the effects of surface Al in the support on the Ir–Re structure and their catalytic behavior in glycerol hydrogenolysis. The Ir–Re interaction is greatly inhibited because of the stronger interaction between Re species and (Si-)Al-OH sites on ASA surface, resulting in the appearance of highly dispersed Re clusters and large Ir crystals after reduction. The barely synergy between the isolated Ir and Re metals in addition to the decreased metal dispersion restrains the glycerol hydrogenolysis reaction over Ir–Re/ASA. On the other hand, the retained mobility of Re species on ‘inert’ D-ASA supports offers the intimate contact between Ir and Re species and hence the formation of Ir–Re alloy catalysts after reduction, promoting greatly the synergy between Ir and Re species in glycerol hydrogenolysis.