Glycerol Dehydration Reaction Research Articles

Combining structure design and surface modification of BPO4 solid acid catalyst to boost the anti-coking performance in dehydration reaction of glycerol

Catalytic vapor-phase dehydration of glycerol is an energy-efficient and environmentally friendly route for producing acrolein, a valuable organic chemical intermediate. However, anti-coking is one of the key problems due to the excessively acid catalytic sites and sluggish mass transfer, restricting the industrial application of this reaction. Herein, potassium element modified BPO4 monolithic foams with the hierarchically porous structure were synthesized by adding potassium element in the gel precursor of BPO4. The catalyst introducing 3% K exhibited the best acrolein selectivity of 81.0% with nearly complete glycerol conversion. In a 10-hour run of the reaction at 320 °C, the selectivity of acrolein could remain at 75.9% with 94.5% glycerol conversion, indicating the superior stability. The excellent activity and stability for 3% K-BPO4 is mainly attributed to the synergetic effect between hierarchical structure providing favorable mass transfer and appropriate acid catalytic sites inhibiting over dehydration reaction. They not only boost activity but also reduce coking, providing a unique approach for the design of solid acid catalyst.

Glycerol dehydration catalyzed by solid acid in nonthermal plasma and simulation analysis of plasma electric field

AbstractNonthermal plasma (NTP), for the first time, was integrated in glycerol dehydration reaction catalyzed by silicotungstic acid supported on mesoporous silica with argon as the carrier and discharge gas. A range of reaction temperatures (220–320°C) and NTP discharge field strengths (2.06–6.87 kV/cm) were studied for the individual and interactive effects regarding the glycerol conversion and product selectivity. Results showed that the presence of NTP always improved the glycerol conversion, and NTP increased acrolein selectivity if properly conditioned. An optimal condition of 275°C and 4.58 kV/cm NTP field strength achieved a glycerol conversion of 94.4 mol%, acrolein selectivity of 88.0 mol%, with an acrolein yield of 83.1 mol%, representing a 10% improvement in acrolein production over that conducted at the same temperature but without NTP. Results of this study will also have significant implication for other heterogeneously catalyzed dehydration reactions. Simulation of the high‐voltage electric field distribution as function of NTP electrical conductivity and relative permittivity of catalyst materials also offers insight for the future design of reactors and catalysts.

Microwave-Assisted Facile Sol–Gel Synthesis of WO3-Based Silica Catalysts for Enhanced Activity in Glycerol Dehydration

WO3 is a promising catalyst for the production of acrolein from glycerol due to its high activity and selectivity. In this study, various metal oxides (W, Zr, and Nb) over colloidal silica (cSiO2) catalysts were obtained using a novel microwave-assisted synthesis method. The enhancement in the sol–gel grafting of metal oxides onto the cSiO2 support was achieved by microwave irradiation (MW) and compared to the conventional heating (CH). WO3-cSiO2 catalysts synthesized by microwave-assisted facile sol–gel synthesis were tested in the gas-phase glycerol dehydration reaction. The best catalytic performance (52.4% acrolein yield) was obtained over a 25%W-cSiO2 sample prepared by the MW method. The best yield results were obtained with a B/(B + L) ratio over 0.50 and with an optimum medium-strength acidity. The activity loss was correlated with the high-strength surface acidity.

Effect of Cu and Sb active sites on the acid–base properties and reactivity of hydrated alumina for glycerol conversion by dehydrogenation and dehydration reactions

Bifunctional Cu–Sb containing catalysts supported on hydrated alumina prepared by different methods were evaluated for glycerol dehydrogenation and dehydration reaction in the gas phase.

Mechanistic investigation of B12-independent glycerol dehydratase and its activating enzyme GD-AE.

B12-Independent glycerol dehydratase (GD) is a glycyl radical enzyme in the biotransformation of glycerol to 1,3-propanediol. GD requires the activating enzyme GD-AE to initiate the radical reaction. GD-AE belongs to the radical S-adenosyl-L-methionine (SAM) enzyme superfamily. However, a previous study showed that GD-AE cleaves SAM unconventionally to generate 5'-deoxy-5'-methylthioadenosine. Herein, we show that GD-AE actually cleaves SAM to form 5'-deoxyadenosine, similar to other radical SAM enzymes. Furthermore, with the synthesized glycerol analogue 2-deoxy-2-fluoroglycerol, we demonstrate that B12-independent GD catalyzes the glycerol dehydration reaction by direct elimination of the C-2 hydroxyl group of a ketyl radical rather than 1,2-OH migration.

Soft-templating routes for the synthesis of mesoporous tantalum phosphates and their catalytic activity in glycerol dehydration and carbonylation reactions

The craftsmanship in catalyst synthesis becomes very fascinating when the catalytic activity of the material can be enhanced by tuning the synthesis conditions. The underlying fundamental strategy is presented here in tailoring the structural and chemical behavior of the tantalum phosphates (TaP) by using different structure directing agents (SDAs). We found that by employing appropriate template assisted pathway it is possible to tune the morphology and the nature of active sites of TaP. The synthesised catalysts were comprehensively characterised by N2-physisorption, FESEM, HRTEM, powder XRD, FTIR, UV–Vis, XPS, NH3 and CO2-TPD, Py-adsorbed IR, elemental analysis and 31P{1H} NMR techniques. The FESEM and HRTEM analysis revealed the transition of non-spherical to rod-shaped particles upon moving from ionic to non-ionic surfactants. The TPD and Py-IR studies revealed the variation in amount, strength and nature of the acidic-basic sites with the change in SDA. The resultant TaP catalysts were investigated for gas phase glycerol dehydration to acrolein and liquid phase glycerol carbonylation to glycerol carbonate. Among these catalysts, TaPC synthesized by using CTAB as SDA exhibited promising catalytic activity in both gas and liquid phase reactions. The active site elucidation in TaPC catalyst was done by adopting basic probe molecule 2,6-lutidine. The deactivation kinetic study was carried out for the gas phase glycerol dehydration reaction. The investigation on the spent catalyst showed it is stable under both gas-phase and liquid-phase reaction conditions. This study hence provides a pathway for analytical architecture and construction of highly efficient TaP catalysts for glycerol transformation reactions.

Glycerol Valorization over ZrO2-Supported Copper Nanoparticles Catalysts Prepared by Chemical Reduction Method

Copper nanoparticles (NPs) and ZrO2-supported copper NPs (Cu NPs/ZrO2) were synthesized via a chemical reduction method applying different pH (4, 7 and 9) and evaluated in a glycerol dehydration reaction. Copper NPs were characterized with transmission electron microscopy (TEM) and UV–vis spectroscopy. Transmission electron microcopy (TEM) results revealed a homogeneous distribution of copper NPs. A hypsochromic shift was identified with UV–vis spectroscopy as the pH of the synthesis increased from pH = 4 to pH = 9. Zirconia-supported copper NPs catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD) and N2O chemisorption. The presence of ZrO2 in the chemical reduction method confirmed the dispersion of the copper nanoparticles. X-ray diffraction indicated only the presence of tetragonal zirconia patterns in the catalysts. XPS identified the Cu/Zr surface atomic ratio of the catalysts. TPR patterns showed two main peaks for the Cu NPS/ZrO2 pH = 9 catalyst; the first peak between 125 and 180 °C (region I) was ascribed to more dispersed copper species, and the second one between 180 and 250 °C (region II) was assigned to bulk CuO. The catalysts prepared at pH = 4 and pH = 7 only revealed reduction at lower temperatures (region I). Copper dispersion was determined by N2O chemisorption. With NH3-TPD it was found that Cu NPs/ZrO2 pH = 9 exhibited the highest total quantity of acidic sites and the highest apparent kinetic constant, with a value of 0.004 min−1. The different pH applied to the synthesis media of the copper nanoparticles determined the resultant copper dispersion on the ZrO2 support, providing active domains for glycerol conversion.

Catalytic Deactivation of HY Zeolites in the Dehydration of Glycerol to Acrolein

The study of the deactivation of HY zeolites in the dehydration reaction of glycerol to acrolein has represented a challenge for the design of new catalysts. HY zeolites with SiO2/Al2O3 molar ratios between 3.5 and 80 were studied. The solids were characterized by XRD, N2 physisorption, SEM-EDXS, Raman and UV-vis spectroscopies, infrared spectroscopy of pyridine (FTIR-Py) and catalytic activity tests from 250 °C to 325 °C. It was found that the total amount of acid sites per unit area of catalyst decreased as the SiO2/Al2O3 molar ratio increased from 3.5 to 80, resulting in the decrease in the initial glycerol conversion. The initial acrolein selectivity was promoted with the increase of the Brønsted/Lewis acid sites ratio at any reaction temperature. The deactivation tests showed that the catalyst lifetime depended on the pore structure, improving with the presence of large surface areas as evidenced by the deactivation rate constants. The characterization of the deactivated catalysts by XRD, N2 physisorption and thermogravimetric analysis indicated that the deposition of coke resulted in the total obstruction of micropores and the partial blockage of mesopores. Moreover, the presence of large mesopores and surface areas allowed the amount of coke deposited at the catalyst surface to be reduced.

Recent Progress in the Understanding and Engineering of Coenzyme B12-Dependent Glycerol Dehydratase.

Coenzyme B12-dependent glycerol dehydratase (GDHt) catalyzes the dehydration reaction of glycerol in the presence of adenosylcobalamin to yield 3-hydroxypropanal (3-HPA), which can be converted biologically to versatile platform chemicals such as 1,3-propanediol and 3-hydroxypropionic acid. Owing to the increased demand for biofuels, developing biological processes based on glycerol, which is a byproduct of biodiesel production, has attracted considerable attention recently. In this review, we will provide updates on the current understanding of the catalytic mechanism and structure of coenzyme B12-dependent GDHt, and then summarize the results of engineering attempts, with perspectives on future directions in its engineering.

Gas-phase dehydration of glycerol to acrolein over different metal phosphate catalysts

We conducted a comparative study of gas phase dehydration of glycerol to acrolein over aluminium phosphate, iron phosphate and nickel phosphate catalysts prepared by a simple replacement reaction method (AlP, FeP and NiP). The textural properties, acid amounts, acid types, and coke contents of the samples were studied. The results showed that all metal phosphate catalysts remained in an amorphous state. The glycerol conversion was proportional to the acid amount of metal phosphate catalyst in the glycerol dehydration reaction. Higher value of B/L was more likely to produce acrolein. Among the metal phosphate catalysts, FeP showed superior performance due to its suitable textural and acid properties. After 2 h on stream, high glycerol conversion (96%), acrolein selectivity (82%) and acrolein yield (79%) were achieved on the FeP catalyst at 280 °C. The catalyst deactivation was ascribed to carbon deposition on the catalyst surface blocking the active sites during the glycerol dehydration reaction.

Catalytic Dehydration of Glycerol to Acrolein over Aluminum Phosphate Catalysts

Gas phase conversion of glycerol to acrolein over a variety of aluminum phosphate (AlP) catalysts synthesized by a simple replacement reaction method with a variation in calcination temperature (300-700 oC, AlP-300, AlP-400, AlP-500, AlP-600, and AlP-700, respectively) has been investigated. The textural properties, acidities and coke contents of the samples were also determined. The catalysts were presented in an amorphous state when the AlP sample was calcined below 500 oC. Further increasing the calcination temperature promoted the formation of orthorhombic α-AlPO4 crystal. The weak acid sites increased when the calcination temperature was raised from 300 to 500 oC. However, the weak acid sites decreased when the AlP was calcined above 500 oC. The acidity of the catalyst played a crucial role in the glycerol dehydration reaction. The maximum acrolein selectivity of 66% at 98% glycerol conversion was obtained over AlP-500 catalyst, due to the largest number of acid sites and appropriate textural properties. AlP-700 exhibited the lowest glycerol conversion, owing to the formation of orthorhombic α-AlPO4 crystalline phase and the lowest amount of acid sites under high calcination temperature. The significant reduction in the acidity of the used sample led to a decrease of glycerol conversion.

Glycerol dehydration over micro- and mesoporous ZSM-5 synthesized from a one-step method

Abstract In this work, ZSM-5 zeolites with low Si/Al ratios (25, 50 and 75) were synthesized with a one-step synthesis method and used for the gas-phase glycerol dehydration reaction. The catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), N2 adsorption-desorption, scanning electron microscopy (SEM), thermogravimetric analyses (TGA) and temperature programmed desorption of ammonia (NH3-TPD). According to the characterization results, crystalline ZSM-5 zeolites with micro- and mesopores were obtained by the one-step synthesis method. Differences in acidity, related to the Si/Al ratios variation, were observed. The zeolite with Si/Al ratio of 25 showed the best performance during 4 h of the glycerol dehydration reaction with the acrolein selectivity remaining around 70%. The fast diffusion of species in the mesopores and high acidity of the synthesized ZSM-5 favored the acrolein formation from the glycerol dehydration.

Synthesis and characterization of a mesoporous cerium oxide catalyst for the conversion of glycerol

CeO2 mesoporous materials were synthesized employing the “hard and soft template” technique. Ceria catalysts have been prepared by a nanocasting procedure using SBA-15 and KIT-6 silica-based templates and Pluronic P123 and F127 for the “soft template” technique. The mesoporous CeO2 was characterized by techniques such as N2 physisorption, which confirmed a mesoporous size pore system and transmission electron microscopy, TEM, which confirmed the material ordered pore structure. TGA/DTA analysis was used to determine the loss of weight compared to the temperature before and after the elimination of the template. On the other hand, by means of IR spectroscopy of the Ce-KIT-6 material, the partial elimination of the Si template after the NaOH treatment was confirmed by decreasing the peaks corresponding to the vibration bands of the Si-O-Si linkages. Finally, by temperature-programmed desorption (TPD) of NH3 and CO2, the acid and basic strength of the catalysts were determined, respectively. All samples exhibited much higher total basicity relative to total acidity. The analysis of TPR-H2 showed regions of low temperature (350-400ºC) where the reduction of the bulk is plausible to be initiated and of high temperature (550ºC) of superficial reduction of the ceria.The performance of the catalysts was evaluated in the dehydration reaction of glycerol in gas phase at 320 ºC. The mesoporous CeO2 material was selective to acetol and reached a 100% conversion of glycerol. The catalyst prepared by the “soft template” technique (CeO2-P123) was the most selective to acetol (76%) with a 12% selectivity to acrolein. With the catalyst prepared by the “hard template” technique (Ce-KIT-6), the selectivity towards acetol was 48% and 22% towards acrolein. The acid properties of CeO2 were found to be a determining factor for the selectivity to acetol and acrolein.

Metal–Organic Framework Mediated Synthesis of Small‐Sized γ‐Alumina as a Highly Active Catalyst for the Dehydration of Glycerol to Acrolein

AbstractThe dehydration of glycerol into acrolein was investigated over small‐sized γ‐Al2O3 prepared by a metal–organic framework (MOF) templated method. The particle size of alumina strongly affected the final physicochemical properties of γ‐Al2O3 as well as its catalytic activity. The MOF‐derived, small‐sized γ‐Al2O3 (M‐Al2O3) catalyst exhibited higher stability and higher activity in the glycerol dehydration reaction than conventional bulk γ‐Al2O3 and nanorod γ‐Al2O3 owing to enriched intercrystal mesopores and an abundance of accessible acid sites. M‐Al2O3 retained its high glycerol conversion (over 80 %) for nearly 200 h, whereas high acrolein selectivity (74 %) was achieved.

Effect of the treatment with H3PO4 on the catalytic activity of Nb2O5 supported on Zr-doped mesoporous silica catalyst. Case study: Glycerol dehydration

We have previously demonstrated the influence of the niobium species over the glycerol dehydration reaction and how the catalyst regeneration by thermal treatment modified the catalytic performance due to the transformation of superficial niobium species. This experimental conclusion encouraged us to find a way to maintain and even improve the catalytic behavior of these Nb-based catalysts. Thus, herein, it is reported the influence of phosphoric acid treatment on 8wt% Nb2O5 supported on a zirconium doped mesoporous silica (Si/Zr=5 molar ratio) catalyst, varying the Nb/P molar ratio between 0.1 and 1. Catalysts were full characterized and tested in the glycerol dehydration at 325°C. This acid treatment modifies the nature of species present on the catalyst surface, as inferred from 31P NMR data, where the presence of zirconium hydrogenphosphate was detected. A comprehensive study of the influence of acid properties on the catalytic activity has been carried out. Thus, the selectivity to acrolein was improved, which was attributed to this hydrogenphosphate phase and the catalyst stability was associated to the existence of acid sites of low and moderate strength. The best catalyst was studied at higher reaction temperatures, showing the highest glycerol conversion and achieving an acrolein selectivity of 74%, at 350°C. This catalyst was also regenerated, maintaining its catalytic activity.

Thermo-kinetic and diffusion studies of glycerol dehydration to acrolein using HSiW-γ-Al2O3 supported ZrO2 solid acid catalyst

The thermo-kinetic study of gas-phase glycerol dehydration reaction using a supported γ-Al2O3 nanoparticle based solid catalyst (SiW20-Al/Zr10) has been investigated. The kinetic model was established based on the reaction mechanism, taking into account two parallel reactions of glycerol degradation into acrolein or acetol. Reaction rate constants and activation energies for all the products in the glycerol dehydration reaction were determined at various reaction temperatures (280–340 °C). The first-order kinetic model and the experimental data fitted-well. Also, based on thermodynamic analysis the values of ΔH‡, ΔS‡, and ΔG‡ for all the endothermic reactions were determined by Eyring equation. Finally, the absence of internal and external diffusions were confirmed by Weisz-Prate Criterion (CWP <1) and Mear's Criterion (CM < 0.15), respectively for pellet diameters less than dP < 5 μm. The results from this study are useful for future reactor modeling and simulation work.

Pore Condensation in Glycerol Dehydration: Modification of a Mixed Oxide Catalyst

Pore condensation has been suggested as an initiator of deactivation in the dehydration of glycerol to acrolein. To avoid potential pore condensation of the glycerol, a series of WO3 supported on ZrO2 catalysts have been prepared through thermal sintering, with modified pore systems. It was shown that catalysts heat treated at temperatures above 800 °C yielded suitable pore system and the catalyst also showed a substantial increase in acrolein yield. The longevity of the heat-treated catalysts was also improved, indeed a catalyst heat treated at 850 °C displayed significantly higher yields and lower pressure-drop build up over the 600 h of testing. Further, the catalyst characterisation work gave evidence for a transition from monoclinic to triclinic tungsten oxide between 850 and 900 °C. There is also an increase in acid-site concentration of the heat-treated catalysts. Given the improved catalyst performance after heat-treatment, it is not unlikely that pore condensation is a significant contributing factor in catalyst deactivation for WO3 supported on ZrO2 catalysts in the glycerol dehydration reaction.

Kinetic Study on Catalytic Conversion of Glycerol to Renewable Acrolein

Biodiesel is a suitable alternative to gasoline and diesel since it emits less carbon emission. There has been a surplus of glycerol in the market due to biodiesel production. Glycerol may be a good source of bio-based feed since it is from a renewable source. The kinetic study of gas-phase glycerol dehydration reaction using a supported ?-Al2O3 nanoparticle based solid heteropoly acid catalyst (SiW20-Al/Zr10) has been investigated. A kinetic model was established, based on the reaction mechanism, taking into account two parallel reactions of glycerol degradation into acrolein or acetol. All the reaction rate constants and activation energies were determined at various reaction temperatures (280 – 340 °C). The first-order kinetic model and the experimental data fitted-well. Results revealed that all the rate constants increased with temperature, and the activation energies of glycerol dehydration to acrolein and acetol were 46.0 and 53.3 kJ/mol. The results from this study are useful for simulation and process modelling of a bio-refinery for sustainable production of bio- based chemicals.

Alternative route for the synthesis of high surface-area η-Al2O3/Nb2O5 catalyst from aluminum waste

This paper describes an alternative route for the production of a high-surface-area ɳ-Al2O3/Nb2O5 catalyst synthesized from aluminum waste and niobium ammonium oxalate (NH4H2[NbO(C2O4)3]·3H2O). The effects of thermal treatment on the morphology and crystal structure were examined by X-ray powder diffraction (XPD), surface area measurements (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence, dynamic scanning calorimetry (DSC) and thermogravimetry (TG) measurement. The catalysts were evaluated in the glycerol dehydration reaction. Catalytic tests were carried out with reactants in gas-phase with a fixed-bed reactor at 300° and 400 °C.

Hierarchical ZSM-5 Zeolite Synthesized by an Ultrasound-Assisted Method as a Long-Life Catalyst for Dehydration of Glycerol to Acrolein

This paper presents a facile and economical route to synthesizing hierarchical porous ZSM-5 zeolite (HP-ZSM-5) by an ultrasound-assisted method as a long-life catalyst for the glycerol dehydration reaction, which is an important reaction for the sustainable production of acrolein from biobased glycerol. The systematic characterizations indicate that the HP-ZSM-5 catalyst possesses large intracrystal mesopores and abundant accessible acid sites. The ultrasonic treatment and violent stirring play a critical role in the synthesis process. Compared with commercial ZSM-5 zeolite (C-ZSM-5), the turnover-frequency value at time zero of the HP-ZSM-5 catalyst increased nearly 1 times, and the lifetime of the HP-ZSM-5 catalyst was prolonged 9 times. The HP-ZSM-5 catalyst exhibits a slower coking rate with higher coke tolerance, the coke preferentially form inside the intracrystal mesopores, and the ratio of hardly removed graphitic carbon is lower than that of C-ZSM-5. The HP-ZSM-5 catalyst exhibits prominent stabi...