Sulfated Zirconia Catalysts Research Articles

Effect the solvent evacuation mode on the catalytic properties of nickel-modified sulfated zirconia catalysts: n-hexane isomerization

This work studies the effect of the evacuation mode of the solvent to optimize the catalytic performances of sulfated zirconia doped with nickel prepared by the sol gel method in one step. Aerogel and xerogel catalysts exhibit different textural, structural and catalytic properties at various calcination temperatures. Aerogels, obtained by drying under supercritical conditions of solvent, exhibit a developed specific surface area and stabilize zirconia tetragonal phase before heating and even at high calcination temperature. However, xerogels obtained by ordinary drying in an oven are amorphous and has a low surface area and weak porosity. XPS spectroscopy shows that the nickel in aerogels is more reducible than those in xerogels. Aerogels exhibit higher activity than the xerogels, in the n-hexane isomerization reaction.

Isomerization of n-butane over Pd–SO4/ZrO2 catalyst: Prospects for commercial application

Increase in productivity of the refineries and improvement the fuel quality demands to engage isobutane as a key feedstock for producing both alkylates and oxygenated additives. Substantial growth of isobutane output via isomerization of n-butane poses a real technological challenge. The goal of this study is to investigate performance of Pd promoted sulfated zirconia catalysts (Pd–SZ) in n-butane isomerization. The physical–chemical characteristics of various anion-modified zirconia catalysts (XRD and IR spectra, BET surface) are presented. It was observed that Lewis acid sites of medium and strong strength and two types of Brönsted acid sites exist. Approximately 90–97% of zirconia is in tetragonal phase.The influence of parameters on conversion of n-butane and selectivity towards isobutane was investigated by varying the temperature (90–290°C), pressure (15–26bar), WHSV (0.5–5h−1), and molar ratio H2/C4 (0.08–3). Mainly, temperature and H2/C4 ratio are responsible for increasing the effectiveness of the process. At H2/С4=0.08–0.3 the apparent activity of Pd–SZ catalyst was high enough to reach the equilibrium conversion of n-butane to isobutane at 140°С value, that is, ∼65%. The best results were obtained on Pd–SZ granules in the form of 2mm trilobe. Water impact and the catalyst lifetime were studied in the pilot setup. Endurance testing of Pd–SZ catalyst in course of 90h showed its sustained operation at H2O concentration up to 20ppm without loss of activity.The estimated process specifications on Pd–SZ catalyst were compared to a conventional process; potential benefits of making use Pd–SZ catalyst are emphasized and discussed.

Mesoporous nanocrystalline sulfated zirconia synthesis and its application for FFA esterification in oils

Mesoporous nanocrystalline sulfated zirconia catalyst has been prepared from zirconium hydroxide synthesized at different digestion/hydrothermal treatment times. Sulfuric acid and chlorosulfonic acid were used as two different sulfonating agents. The effect of digestion time, sulfonating agent and the calcination temperature on structural, textural and catalytic properties of the prepared catalyst were investigated in details using nitrogen adsorption–desorption (BET), ammonia temperature programmed desorption (NH3-TPD), X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TGA–DSC), and Fourier transform infrared spectroscopy (FTIR). The sulfated zirconia prepared at various digestion times and two different sulfonating agents were tested for the esterification of free fatty acid (FFAs) in soybean oil (prepared by mixing oleic acid in soybean oil) as model reaction. Sulfated zirconia catalyst prepared with 3h digestion time and 600°C calcination temperature using chlorosulfonic acid showed the highest catalytic activity with about 85% conversion in just 80min of esterification time at 60°C reaction temperature.

Preparation and properties of sulfated zirconia for hydrolysis of ethyl lactate

Sulfated zirconia catalysts are proposed for the reversible hydrolysis of ethyl lactate instead of liquid acids. Sulfated zirconia catalysts were prepared by precipitation-impregnation method. The zirconium hydroxide was produced from zirconium oxychloride by adding aqueous ammonia and then impregnated in sulfuric acid. The solid samples were obtained by filtration and evaporation of the mixtures, respectively. After the samples were calcined, the sulfated zirconia catalysts were prepared. The results showed that the catalyst prepared by evaporation has higher catalytic activity. The physicochemical characteristics of the sulfated zirconia catalysts were studied by thermal analysis, X-ray powder diffraction (XRD), temperature programmed desorption of ammonia (NH3-TPD) and N2 adsorption-desorption, respectively. By the precipitation-impregnation-evaporation method, the optimal sulfated zirconia catalyst of tetragonal phase was prepared under liquid-solid ratio of 5ml/g, 1 mol/L of H2SO4 and calcination at 650 °C for 3 h. The conversion of the ethyl lactate was 87.8% in 3 h at 85 °C with the catalyst loading 2 wt% and initial molar ratio of water to ethyl lactate 20: 1.

Synthesis of biolubricants using sulfated zirconia catalysts

Synthesis of biomass-derived lubricants via esterification, transesterification, and simultaneous reactions of both was studied by using sulfated zirconia catalysts. Soybean oil or free fatty acids derived from soybean oil were used as a biomass-derived resource for the synthesis of biolubricants. Long chain alcohols (carbon number≥8) or neo-polyols (e.g., 2,2-diethyl-1,3-propanediol, trimethylol propane, pentaerythritol) were used as co-reactants. The structure of the alcohol significantly affected the conversion and yield for the esterification with oleic acid. The esters produced showed kinematic viscosity and viscosity index comparable to commercial lubricants. Various sulfated zirconia catalysts were prepared and were characterized by X-ray diffraction, NH3 temperature-programmed desorption, Brunauer–Emmett–Teller isotherm, and tested for esterification. The type of zirconium precursor demonstrated a significant effect on the physical property of the catalyst and its catalytic activity. Interestingly, esters with fully saturated hydrocarbon chains were synthesized from unsaturated free fatty acids regardless of the absence of hydrogen gas. The sulfated zirconia could be recycled for up to five repeated reactions without any degradation. The effects of reaction time and temperature were also investigated.

PH control of the structure, composition, and catalytic activity of sulfated zirconia

We report a detailed study of structural and chemical transformations of amorphous hydrous zirconia into sulfated zirconia-based superacid catalysts. Precipitation pH is shown to be the key factor governing structure, composition and properties of amorphous sulfated zirconia gels and nanocrystalline sulfated zirconia. Increase in precipitation pH leads to substantial increase of surface fractal dimension (up to ∼2.7) of amorphous sulfated zirconia gels, and consequently to increase in specific surface area (up to ∼80m2/g) and simultaneously to decrease in sulfate content and total acidity of zirconia catalysts. Complete conversion of hexene-1 over as synthesized sulfated zirconia catalysts was observed even under ambient conditions.

Liquid-phase dehydration of sorbitol to isosorbide using sulfated zirconia as a solid acid catalyst

Sulfated zirconia catalysts have been prepared with zirconium (IV) hydroxide and sulfuric acid as the sources of zirconia and sulfate group, respectively. In this study, liquid-phase dehydration of sorbitol to isosorbide is investigated in the presence of the catalysts under various reaction conditions including reaction temperature, time, catalyst dosage and sulfur content/acidity of the catalysts. The results show that sulfated zirconia, with high sulfur content and a tetragonal crystalline structure, is a promising solid acid catalyst that can be used at least four times in the dehydration of sorbitol to isosorbide.

Sulfated zirconia; an efficient and reusable acid catalyst for the selective synthesis of 4-phenyl-1,3-dioxane by Prins cyclization of styrene

Prins cyclization of styrene with paraformaldehyde was carried out over sulfated zirconia (SZ) catalyst in liquid phase. The SZ catalysts were synthesized by precipitation method with different sulfur impregnation and characterized by XRD, FT-IR, Nitrogen sorption, NH3-TPD. The SZ showed best performance among different types of acid catalysts. The acidity of SZ optimized by different concentrations of H2SO4 treatment influences the selectivity for dioxane. The sulfur loading, nature of solvent, temperature, catalyst amount, mole ratio and reusability of catalyst were investigated. The SZ catalyst synthesized by impregnating 2N sulfuric acid was found to be highly selective for the synthesis of 4-phenyl-1,3-dioxane (93%) with almost complete conversion of styrene (∼100%). The catalyst was recycled thrice with negligible decrease in the yield of 4-phenyl-1,3-dioxane.

Process optimization and kinetic study for biodiesel production from non-edible sea mango (Cerbera odollam) oil using response surface methodology

This paper presents the process optimization and kinetic study for the heterogeneous transesterification of non-edible sea mango (Cerbera odollam) oil using response surface methodology central composite design (RSMCCD). The four transesterification process variables studied are; reaction temperature (333–453K), reaction time (1–5h), molar ratio of oil to methanol (1:6–1:14) and amount of sulfated zirconia catalyst (2–10g*g−1) (catalyst/oil). From this study, it was found that reaction temperature gave the most significant effect on the conversion of sea mango oil to fatty acid methyl esters (FAME), followed by reaction time. There were also significant interaction effects between reaction temperature and amount of catalyst, and between reaction time and amount of catalyst. Based on the optimized condition, highest conversion of 97.5% was predicted using the following variables; reaction temperature=423K, reaction time=3h, molar ratio of oil to methanol=1:12 and amount of catalyst=8g*g−1. Experimental verification on the predicted optimum condition gave an actual conversion of 94.1%. The small error between the predicted and actual optimum conversion (3.5%) indicated that the model was valid and accurate in representing the actual experimental values and also in predicting conversion at any condition within the range studied. The developed kinetics model suggested a 1.1th order reaction with activation energy of 36.03kJmol−1 and frequency factor of 5.56×102min−1.

Sulfated Zirconia Catalysts for Low Temperature Isomerization of n-Pentane

UNCONVENTIONAL sulphated zirconia (SZ) catalysts were .….. prepared and examined for n-pentane isomerisation in this investigation. The sulfation was performed using H

Effects of calcination temperature and water-washing treatment on n-hexane hydroisomerization behavior of Pt-promoted sulfated zirconia based catalysts

Synthesis of Pt-promoted sulfated zirconia catalyst Pt/SO42−/ZrO2 (designated as PSZ), Pt/SO42−/ZrO2-Al2O3 (designated as PSZA), and Pt/SO42−/ZrO2-Al2O3-Y2O3 (designated as PSZAY) was reported. These catalysts were characterized by N2 adsorption–desorption, thermal gravimetric (TG) analysis, NH3-temperature programmed desorption (NH3-TPD), and H2-temperature programmed reduction (H2-TPR) techniques. Effects of calcination temperature of the catalysts on the n-hexane hydroisomerization behavior were investigated in details. The experiment results revealed that the addition of Al and Y or Al promoter alone could improve the thermal stability of the catalysts. PSZA and PSZAY exhibited higher isomerization activity than unmodified PSZ as the calcination temperature of sulfated Zr(OH)4 was relatively high, for example, between 650°C and 750°C. For the first time, it was found that water-washing treatment of PSZA and PSZAY at different preparation stages had considerably different impacts on their catalytic activity. Water-washing after calcination of the sulfated Zr(OH)4, the catalytic activity of PSZA and PSZAY was high, as indicated by approximately 80% of n-hexane conversion. However, water-washing before calcination of sulfated Zr(OH)4 led to a significant decrease in the catalytic activity of PSZA and PSZAY, that is, the n-hexane conversion diminished to around 35%. It was proposed that the presence of excessive sulfur species over sample was favorable for keeping the active sulfur species in the catalyst surface.

Hydrodechlorination of dichloromethane with mono- and bimetallic Pd–Pt on sulfated and tungstated zirconia catalysts

Monometallic (Pt or Pd) and bimetallic (Pt–Pd) catalysts supported on zirconia promoted with sulfate (SZ) or tungsten oxide (WZ) were prepared and tested in the gas-phase hydrodechlorination of dichloromethane. The catalysts showed a high selectivity to non-chlorinated products (between 80% and 90% at 250°C) being methane the main reaction product. As a general trend, the WZ catalysts yielded significantly higher dichloromethane conversion than the SZ ones, yielding all the catalysts initial conversions higher than 80% at a reaction temperature of 250°C. However, the former showed a very poor stability regardless of the metallic active phase. On the other hand, the presence of palladium in the sulfated zirconia catalyst avoids deactivation as proved in long-term experiments (80-h time on stream). XPS and elemental analyses of the used catalysts suggest that adsorption of organochlorinated species is a cause of deactivation by blocking the active sites. In the monometallic SZ Pt catalyst, deactivation occurs also by poisoning of the Pt sites by the H2S resulting from sulfate reduction under the hydrogen-rich gas atmosphere. The metal particle size appears to be a critical point with regard to stability of the catalysts. The one with the highest dispersion showed the highest stability with no signs of deactivation after more than 80h on stream.

Preparation of highly superacidic sulfated zirconia via combustion synthesis and its application in Pechmann condensation of resorcinol with ethyl acetoacetate

A novel zirconia-based catalyst, with high sulfur content (15% w/w) and preservation of the tetragonal phase of zirconia, was synthesized for the first time via a solution combustion synthesis approach. Such high sulfur content with preservation of the tetragonal phase has not been reported so far. The catalyst synthesis parameters were optimized using a probe reaction of Friedel–Crafts alkylation. The optimized catalysts, fuel-lean sulfated zirconia (FLSZ) and fuel-rich sulfated zirconia (FRSZ), were characterized by XRD, FTIR, TPD, EDAX, SEM, and BET surface area and pore size analysis. Further, the activity and stability of FLSZ was tested using a Pechmann condensation reaction between resorcinol and ethyl acetoacetate to produce 7-hydroxy 4-methyl coumarin selectively. A complete theoretical and experimental analysis is presented, and a kinetic model is developed for this reaction. The model explains the experimental data well. The characterization and reaction studies show that combustion-synthesized sulfated zirconia exhibits higher superacidity than the conventional sulfated zirconia catalyst.

Comparison in Catalytic Activities of Sulfated Zirconia and Sulfated Tin Oxide for Converting Free Fatty Acids in Crude Palm Oil to Their Methyl Esters

For the first time, the catalytic activities of sulfated zirconia and sulfated tin oxide have been directly compared for esterification of free fatty acids (FFA) in crude palm oil to produce fatty acid methyl esters (FAME). Both sulfated zirconia and sulfated tin oxide catalysts were prepared by hydroxide precipitation, followed with impregnation using sulfuric acid as the source of sulfate. The concentrations of sulfuric acid were varied. The sulfated zirconia and sulfated tin oxide catalysts were characterized by XRD, nitrogen adsorption, elemental analysis, FTIR and potentiometric titration. Esterification of FFA in crude palm oil was carried out in a stirred-tank reactor equipped with a reflux condenser. The influences of the amount of methanol and catalysts were investigated. The results have revealed that both sulfated zirconia and sulfated tin oxide well catalyze the esterification of FFA to produce FAME. Sulfated tin oxide is, on average, 2 times more active than sulfated zirconia. Increasing the concentration of sulfuric acid used in the preparation of both catalysts results in higher sulfur contents and greater acidities of the catalysts. As a result, the conversions of FFA increase. Moreover, the conversions of FFA have been found to increase with the amounts of methanol and catalysts up to certain values and then level off.

Transesterification of palm oil and crude sea mango (Cerbera odollam) oil: The active role of simplified sulfated zirconia catalyst

This study was conducted to investigate the active role of sulfated zirconia catalyst in the transesterification of palm ( Elaeis guineensis ) and sea mango ( Cerbera odollam ) oils. Initially, the sulfated zirconia catalysts were prepared and optimized under various preparation conditions – calcination temperature, calcination period and ratio of Zr-species/support - and then characterized for its physical and chemical properties. The performance of the sulfated zirconia catalysts was tested in the transesterification of palm oil and sea mango oil. The optimized sulfated zirconia catalyst was also tested for its reusability and regenerability. From this study, it was found that the best (optimum) sulfated zirconia catalyst was prepared using calcination temperature of 400 °C, calcination period of 2.5 h and ratio of Zr-species/support of 2 g g −1 . It was also found that the prepared sulfated zirconia catalyst contains acid sites which become the key factor in the transesterification process. The optimized sulfated zirconia catalyst was shown to be able to produce high yield of fatty acid methyl esters (>80%) even with oil that has high free fatty acids content i.e. sea mango oil. The reusability and regenerability study showed that the optimized sulfated zirconia can be regenerated and reused repeatedly with an average of 5% loss in activity after each run. ► Investigated the catalytic role of sulfated zirconia in ransesterification. ► Properties of catalyst was affected mostly by calcination temperature. ► High acidity enhances the conversion of high FFA oil.

Simultaneous transesterification and esterification for biodiesel production with and without a sulphated zirconia catalyst

Simultaneous catalysed transesterification of rapeseed oil and esterification of 10wt% myristic acid with methanol was studied using sulphated zirconia and in the absence of catalyst. The maximum total FAME content of 86% was obtained at a catalyst loading of 3wt%, temperature of 170°C, pressure of 22 bars, molar ratio of oil to methanol of 1:20 and stirring rate of 600rpm for 60min. At these conditions, FFA was observed to reach 2.95% (2.94mg/ml sol.). Thermo/catalytic cracking and hydrolysis of triglyceride was presumed to form the FFA. Water was also formed: dehydration of methanol is likely to be the principal source. Three sets of main reactions occurred at distinctly different rates. Esterification of myristic acid was the most rapid reaction. Direct transesterification of triglyceride and side-reactions of thermo/catalytic cracking of triglyceride followed by esterification of fatty acid and hydrolysis of triglyceride followed by esterification of fatty acid occurred afterward. Dehydration of methanol was observed throughout the reaction, producing a constant supply of water, thereby facilitating hydrolysis reactions.

Esterification of caprylic acid with alcohol over nano-crystalline sulfated zirconia

The catalytic activity of nano-crystalline sulfated zirconia catalyst, prepared by sol–gel method and characterized by various analytical tools, was evaluated for the esterification of caprylic acid with different short chain alcohols. The lower concentration of catalyst (0.5 wt%) exhibited 96–98% conversion of caprylic acid with methanol and 100% selectivity for methyl caprylate at 60 °C. The conversion was decreased with increasing carbon chain of alcohols namely with ethanol, n-propanol and n-butanol at 60 °C but increased significantly (91–98%) at higher reaction temperature. The selectivity for respective alkyl caprylate was observed to be 100% irrespective of the alcohol used. The activity of the catalyst was slightly decreased with successive five reaction cycles due to the water formed during the reaction.

Sulfated zirconia: an efficient solid acid catalyst for esterification of myristic acid with short chain alcohols

Sulfated zirconia (SZ) catalysts prepared by a two-step sol–gel method and calcined at 600–700 °C were evaluated for esterification of myristic acid with methanol using varied acid to alcohol ratio, reaction temperature and catalyst concentration. An exceptionally small concentration of SZ catalysts (0.125–0.5 wt% to acid) exhibited 98–100% conversion of myristic acid with methanol at 60 °C after 5 h. The conversion was decreased with an increase in the alkyl chain of alcohol from methanol to butanol, however, similar conversion was achieved by increasing the reaction temperature to 90 °C. The ester formation was selective, irrespective of alcohol and other reaction variables. The calcination temperature has strong influence on the structural, textural and acidic features and thus on the activity and re-usability of SZ catalysts. The reaction is sensitive to moisture present in methanol or reaction mixture. The studied reaction is Brönsted acid catalyzed and the SZ catalyst having higher number of Brönsted acid sites was re-used successfully without significant loss in activity; whereas the SZ catalyst having lower number of Brönsted acid sites showed a decrease in activity (∼28%) after five reaction cycles. The results clearly indicated the necessity of higher number of Brönsted acid sites for better performance and recycling of the SZ catalysts for esterification of myristic acid with methanol under the conditions studied.

Sulfated zirconia as a robust superacid catalyst for multiproduct fatty acid esterification

Sulfated zirconia catalysts obtained by employing chlorosulfuric acid show significantly higher activity in the esterification of fatty acids with different alcohols compared with catalysts made using sulfuric acid. The superior performance results from higher sulfur content, larger pores and stronger acid sites. These catalysts are robust and do not leach out sulfonic groups. Catalyst performance depends strongly on the sulfation reagent and the calcination conditions of the intermediate zirconium hydroxide. A series of kinetic experiments was carried out with lauric acid and various alcohols (methanol, 2-ethylhexanol, propanols and butanols). The new catalysts are ca. five times faster when using primary alcohols independent of the alcohol chain length. When using secondary and tertiary alcohols the reaction rate drops considerably. This is explained by a linear free energy relationship of substituent reactivity. The kinetic investigation shows that chlorosulfated zirconia is suitable as a multiproduct catalyst for manufacturing fatty esters, by employing a catalytic reactive distillation process.

Synthesis of dypnone by solvent free self condensation of acetophenone over nano-crystalline sulfated zirconia catalyst

Nano-crystalline sulfated zirconia catalyst, prepared by two-step sol–gel method, has been studied for the solvent free self condensation of acetophenone to dypnone. The influence of calcination temperature on the structural, textural and catalytic activity of sulfated zirconia has been analyzed. The surface acidity along with the structural and textural features of the catalyst influenced its activity. The conversion of acetophenone was found to be effected by the variation in the reaction and calcination temperature, however, the dypnone selectivity was not affected much. The catalyst calcined at 650 °C, showed maximum dypnone selectivity of 92% with 68.2% acetophenone conversion at 170 °C after 7 h. The catalyst was reused up to five cycles with marginal decrease in acetophenone conversion, however, without losing its selectivity for dypnone.