Sulfated ZrO2 Research Articles

Synthesis of acidic modified UiO‐66 by concentrated sulphation form and its application in the production of fatty acids ethyl esters

AbstractIn this article, UiO‐66 metal–organic frameworks containing structural modifications were synthesized and characterized to increase acidic surface behaviour for application in heterogeneous acid catalysis to produce fatty acid ethyl esters (FAEE) from degummed soybean oil. The solvothermal route synthesized UiO‐66, and the post‐synthesis acid modifications were done by sulphation reaction in strong acidic medium. The synthesized materials were characterized by physicochemical techniques such as X‐ray diffraction (XRD), C‐ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectrometer (FTIR), and N2 physisorption, observing a strong structural modification of the original UiO‐66, but no signal of sulphated ZrO2 was presented. However, the acidic characteristics on the material's surface were increased. A central compound centred on face 23 experiments design was carried out to evaluate three essential reaction variables: temperature, time, and alcohol/oil ratio, obtaining an optimized fit for the UiO‐66‐S35 of temperature at 140°C, time of 3 h, and molar ratio of 16. The optimized statistical adjustment was applied in the reuse cycles assays in three catalyst cycles, reaching the maximum yield of 95% in FAEE, keeping the catalyst active at the end of 3 cycles.

Nitration of chlorobenzene by ultrasonic-assisted synthesized sulfated ZrO2 catalyst with NO2

Nitration of chlorobenzene by ultrasonic-assisted synthesized sulfated ZrO2 catalyst with NO2

Fishery waste valorization: Sulfated ZrO2 as a heterogeneous catalyst for chitin and chitosan depolymerization.

Chitin and chitosan are abundant unique sources of biologically-fixed nitrogen mainly derived from residues of the fishery productive chain. Their high potential as nitrogen-based highly added-value platform molecules is still largely unexploited and a catalytic way for their valorization would be strongly desirable within a biorefinery concept. Here we report our results obtained with a series of heterogeneous catalysts in the depolymerization of chitosan and chitin to acetylglucosamine. Copper catalysts supported on SiO2, SiO2-Al2O3, SiO2-ZrO2, ZrO2 and the corresponding bare oxides/mixed oxides were tested, together with a sulfated zirconia system (ZrO2-SO3H) that revealed to be extremely selective towards glucosamine, both for chitosan and chitin, thus giving pretty high yields with respect to the values reported so far (44% and 21%, respectively). The use of a heterogeneous catalyst alone, without the need of any additives or the combination with a mineral acid, makes these results remarkable.

Insight into the promoting effect of support pretreatment with sulfate acid on selective catalytic reduction performance of CeO2/ZrO2 catalysts

In this paper, sulfated ZrO2 were synthesized via precipitation and impregnation method, and the promoting effects of support sulfation on selective catalytic reduction (SCR) performance of CeO2/ZrO2 catalysts were investigated. The results revealed that sulfated ZrO2 could significantly enhance the SCR activity of CeO2/ZrO2 catalysts in a wide temperature range. Especially when S/Zr molar ratio was 0.1, CeO2/ZrO2-0.1S catalyst exhibited a large operating temperature window of 251 ∼ 500 °C and its N2 selectivity was 100 % in the temperature range of 150 ∼ 500 °C. Moreover, CeO2/ZrO2-0.1S catalyst possessed a superior low-temperature activity over 0.1S-CeO2/ZrO2 catalyst. After exposing to 100 ppm SO2 for 15 h, a high NO conversion efficiency of CeO2/ZrO2-0.1S catalyst (90.7 %) could still be reached. The characterization results indicated that ZrO2 treated with a proper dosage of sulfate acid was beneficial to enlarge the specific surface area greatly. Sulfated ZrO2 was also in favor of promoting the transformation of CeO2 from crystalline state to highly-dispersed amorphous state, and inhibiting the transformation of ZrO2 from tetragonal to monoclinic phase. It could also enhance the total surface acidity greatly with an increase in both Brønsted acid sites and Lewis acid sites, thus significantly improving NH3 adsorption on catalyst surface. Besides, the promoting effect of support sulfation on SCR performance of CeO2/ZrO2 catalysts was also related with the enhanced redox property, higher Ce3+/(Ce3++Ce4+) ratio and abundant surface chemisorbed labile oxygen. The in-situ DRIFTS results implied that nitrate species coordinated on the surface of CeO2/ZrO2-0.1S catalyst could participate in the Selective catalytic reduction with ammonia (NH3-SCR) reactions at either medium or high temperature, suggesting that both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms might be followed in SCR reactions.

Oleic acid esterification with methanol to methyl oleate under light irradiation using modified alginate capsules loaded with a solid acid catalyst

Sulfated ZrO2 and amorphous carbon-based solid acid catalysts were prepared by a literature method and were estimated to contain 54 and 240 μmol g-cat−1 acid sites, respectively. The capsule shell was modified by various methods to increase its permeability to oleic acid, and methoxy functionalization of the alginate shell with methanol gave the biggest increase and also improved the oleic acid esterification to methyl oleate by the capsules loaded with the solid acid catalyst. The amount of solid acid catalyst loaded in the capsule was optimized, and the capsules loaded with the amorphous carbon-based solid acid catalyst showed a higher methyl oleate formation rate and yield than the capsules loaded with sulfated ZrO2 and active carbon powder under light irradiation. This is probably because the number of acid sites on the amorphous carbon-based catalyst was greater than that on the sulfated ZrO2 catalyst. In addition, the amorphous carbon-based catalyst was directly heated under light irradiation because it was black, whereas the sulfated ZrO2 catalyst was heated by the reaction media that was heated by the active carbon powder absorbing the irradiated light.

Synthesis of CoO–NiO promoted sulfated ZrO2 super-acid oleophilic catalyst via co-precipitation impregnation route for biodiesel production

Abstract This study focuses on the synthesis of a novel heterogeneous CoO–NiO promoted sulfated ZrO2 (CN/SZ) catalyst and investigating its catalytic efficiency as a transesterification reagent. Catalytic performance has also been compared with two reference catalysts viz., sulfated ZrO2 (SZ) and pure ZrO2 (Z). Prepared materials were characterized using X-ray diffraction (XRD) technique, N2- adsorption/desorption study, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDAX), Raman, Fourier Transformed Infrared (FTIR), and X-ray photoelectron (XP) spectroscopy techniques. Surface acidity and basicity were assessed by NH3 and CO2 temperature-programmed desorption (TPD) respectively that established high surface acidity and basicity of CN/SZ nanocatalyst. The reagent has shown supreme catalytic performance as only 0.2 wt% catalyst loading amount has provided 98.8% of biodiesel yield with 3:1 MeOH:Oil molar ratio at 65 °C for 2 h. Also, the reusability study has proved the efficacy of CN/SZ nanocatalyst that it can successfully be reused in five consecutive reaction cycles displaying promising results and the reactivated catalyst provided remarkably high biodiesel yield of 96.8%. Further, the mechanistic pathway of the simultaneous catalytic esterification of free fatty acid and transesterification of triglyceride occurring on catalyst surface has also been explored.

Liquid crystals as pore template for sulfated zirconia

Porous sulfated zirconia was prepared using a sol-gel process associated with liquid crystal templates (LCTs). Evaluation was made of the effects of the Zr4+:SO42− molar ratio and aging time on the formation and stability of the lyotropic arrangement of the LCT gel and the features of the resulting mesoporous powders. Polarized light microscopy and small-angle X-ray diffraction (SAXD) analysis of the LCT gel revealed the prevalence of hexagonal mesophase (P6mm) in the sulfated samples. Thermal treatment of the samples resulted in sulfated ZrO2 ceramic powders whose infrared spectra exhibited bands characteristic of mono- and bi-dentate SO42− groups bonded to ZrO2. X-Ray diffractograms of the materials showed a mixture of monoclinic and tetragonal phases of zirconia, with the tetragonal phase increasing from 86–90% to 100% as the Zr4+:SO42− molar ratio decreases from 15 to 5. Crystallite sizes of about 9.5 and 4.5 nm were observed for the pristine and sulfated zirconia (Zr4+:SO42− = 5), respectively. The lattice fringe distances observed for selected areas in the electron diffraction patterns and in high-resolution transmission electron micrographs confirmed the mixture of tetragonal and monoclinic crystalline phases. Small-angle X-Ray scattering analysis showed that the gyration radius was around 2 nm and that the particles were organized as a branched network with a fractal surface when sulfate was inserted in the zirconia structure, improving its porous characteristics. The LCT generated pores with greater diameters (up to 4.4 nm) in the sulfated samples, while the surface area increased to 146 m2 g−1. The gel aging process led to the reinforcement of the pore wall structure, prevented shrinkage effects during calcination, and enabled higher surface areas to be achieved. Scanning and transmission electron microscopy analyses showed that the walls of the pores were composed of platelets of irregular shapes, giving rise to mesopores. The porous structure, combined with the presence of acid sites, improved by sulfate groups at the surface of tetragonal zirconia crystallite, makes these materials promising candidates for application as catalysts in dehydration reactions.

Sulfated ZrO2 supported CoMo sulfide catalyst by surface exsolution for enhanced hydrodeoxygenation of lignin-derived ethers to aromatics

Catalytic transformation of lignin is a sustainable way to provide aromatics, which depends on the structure and property of catalytic sites. A bifunctional sulfated ZrO2 supported CoMo sulfide catalyst has been synthesized by in situ exsolution approach. The exsolved CoMo-sZr(exs) catalyst significantly enhanced the initial C–O bond cleavage rate (0.058 mol·g−1·h−1) compared to the impregnated and physically mixed sulfated ZrO2 supported CoMo sulfide catalysts. Notably, the reusability tests also showed that the as-prepared catalyst presented total ethers conversion of 94% with aromatics yield of 86% after four consecutive cycles. This was related to the appropriate sulfide-support interaction, acid sites and highly-dispersed CoMo sulfide, in conformity with the catalyst characterization. Thereby it could facilitate reactant adsorption and effectively break down the C–O bonds in lignin derived fragments to form aromatics. This work points out a new avenue for the design of effective bifunctional catalysts for lignin depolymerization.

Hydro-Pyrolysis and Catalytic Upgrading of Biomass and Its Hydroxy Residue Fast Pyrolysis Vapors

Fast pyrolysis of Miscanthus, its hydrolysis residue and lignin were carried with a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) followed by online vapor catalytic upgrading with sulfated ZrO2, sulfated TiO2 and sulfated 60 wt.% ZrO2-TiO2. The most evident influence of the catalyst on the vapor phase composition was observed for aromatic hydrocarbons, light phenols and heavy phenols. A larger amount of light phenols was detected, especially when 60 wt.% ZrO2-TiO2 was present. Thus, a lower average molecular weight and lower viscosity of bio-oil could be obtained with this catalyst. Pyrolysis was also performed at different pressures of hydrogen. The pressure of H2 has a great effect on the overall yield and the composition of biomass vapors. The peak area percentages of both aromatic hydrocarbons and cyclo-alkanes are enhanced with the increasing of H2 pressure. The overall yields are higher with the addition of either H2 or sulfated catalysts. This is beneficial as phenols are valuable chemicals, thus, increasing the value of bio-oil. The results show that the hydrolysis residue has the potential to become a resource for phenol production.

Application of microwave irradiation for fabrication of sulfated ZrO2\u2013Al2O3 nanocomposite via combustion method for esterification reaction: process condition evaluation

The zirconia–alumina nanocatalyst was prepared using microwave combustion method, and the effects of alumina/zirconia ratio, fuel-to-oxidizer ratio, and calcination temperature on its structural and chemical performance were examined. Furthermore, the most suitable synthesized nanocatalyst was impregnated using different dosages of sulfate group to improve the activity of the sample for the esterification reaction. The results revealed that there was a significant improvement in the crystalline structure of alumina and zirconia for the samples having the alumina/zirconia ratio of 2. It was also noted that some amorphous structures were observed for low fuel dosages, while the activity of the sample was reduced with higher fuel consumption than the stoichiometric ratio, which can be attributed to the increase in the crystallite size and formation of different alumina phases. Based on calcination results, non-considerable changes were observed in the morphology and activity of the catalyst. It can be concluded that the solution combustion method is suitable for nanocatalyst preparation without any requirement of further thermal treatment. In addition, the activity of the sample was enhanced by impregnation with H2SO4 where the conversion of 91.6% was achieved. The catalyst showed high reusability at least for seven times as well as high stability of zirconia–alumina as a support.Graphical abstract

Hydrodeoxygenation of isoeugenol over Ni-SBA-15: Kinetics and modelling

Hydrodeoxygenation (HDO) of isoeugenol has been investigated over Ni-SBA-15 and Ni-SZ-SBA-15 containing sulfated ZrO2 with Si/Zr molar ratio of 8.4. The catalysts were prepared via incipient wetness method and characterized by N2 adsorption, AAS, TPR, X-ray diffraction (XRD), thermal gravimetric/differential thermal analyses (TG-DTA), organic elemental analysis, pyridine adsorption-desorption with Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The results revealed that 75% yield of propylcyclohexane was obtained over a non acidic Ni-SBA-15 in isoeugenol HDO at 300 °C under 3 MPa H2 using dodecane as a solvent. Ni-SZ-SBA-15 gave only very low HDO activity, which is explained by location of the acid sites both inside and outside SBA-15, whereas nickel particles were partially located inside the SBA-15 structure. On the other hand Ni particles in Ni-SBA-15 with the size of 20 nm were located outside SBA-15 promoting HDO. The kinetic model was developed for HDO of isoeugenol based on the proposed reaction network, which took into account formation of intermediate products as well as oligomers. The developed kinetic model was capable of describing well the experimental data with the degree of explanation equal to 91%. The activation energy for hydrogenation of propylcyclohexene and for demethoxylation of dihydroeugenol to 4-propylphenol are equal to 92 kJ/mol and 62 kJ/mol, respectively.

Hydrogenation of Ethanol-Lignin of Larch Wood in Supercritical Ethanol in the Presence of Sulfated Catalysts ZrO2 and Pt/ZrO2

Hydrogenation of Ethanol-Lignin of Larch Wood in Supercritical Ethanol in the Presence of Sulfated Catalysts ZrO2 and Pt/ZrO2

Spectroscopic study of radical cation species formed on sulfated TiO2 upon benzene adsorption

Sulfated TiO2 is well known for its high acidity, which is due to the presence of sulfate ions that create strong Brönsted and Lewis acid sites. The Lewis acid sites can also exhibit oxidizing properties. As previously observed for sulfated ZrO2, the greater the strength of the acid site, the greater the oxidative potential.The oxidative ability can be evaluated by the interaction with a substance with high ionization potential such as benzene. Benzene was adsorbed on sulfated TiO2 at room temperature, and the species formed from the interaction was investigated by Raman and electron spin resonance (ESR) spectroscopy. Resonance Raman spectra of adsorbed benzene showed bands that are distinct from bands observed in the spectra of neutral molecules. Furthermore, from the absorption spectra in the visible and near-infrared it was possible to identify these species as phenylene oligomer radical cations. Also, aromatic radical cations were detected by ESR spectra. Although they were present in small amounts, these cations may be responsible for the bands observed in the Raman spectra because of the resonance Raman effect signal enhancement.

Citrate-mediated sol–gel synthesis of Al-substituted sulfated zirconia catalysts for α-pinene isomerization

Solid acids are desirable heterogeneous catalysts for green chemistry, with zirconia and its sulfated analogues offering tunable Lewis/Brønsted character. A new route to sulfated ZrO2, and Al-substituted ZrO2 (SO4/AlxZrO2), via carbonization and calcination of metal citrate gels and their subsequent sulfation by (NH4)2SO4 is reported. Structural and acidic properties of these materials were characterized by XRD, Raman, XPS, TGA-MS, N2 porosimetry, and propylamine and pyridine titration. Parent and sulfated materials all adopted the tetragonal zirconia phase, with Al-substitution (evidenced by contraction of the zirconia lattice parameter) at between 0.38–3.50wt% increasing the surface area but decreasing acid strength, accompanied by an overall increase in total acid site loading and Lewis character. Low Al concentrations enhance α-pinene isomerization activity by up to 50% due to the increased acid site loading, however the Turnover Frequency (TOF) remained constant indicating a common active site. The TOF decreased for Al concentrations >3.5wt% due to a further fall in acid strength, manifest as higher selectivity to polycyclic versus monocyclic products.

Diols Production From Glycerol Over Pt-Based Catalysts: On the Role Played by the Acid Sites of the Support

A series of 1 wt% AuPt (6:4) catalysts were prepared by sol immobilization using acidic [TiO2, H-Mordenite, SiO2, MCM-41, sulphated ZrO2 (S-ZrO2)] and one basic (MgO) oxide supports. A careful characterization of the catalyst was performed by HRTEM and FTIR spectroscopy. EDX analysis showed that on all catalysts only alloyed AuPt nanoparticles are present, but the final size of AuPt particles is significantly affected by the support. Indeed, on TiO2 the mean AuPt nanoparticles diameter is 3.7 nm, whereas for all the remaining supports, larger AuPt nanoparticles with diameter of 6–7.5 nm were obtained. AuPt catalysts result very active in catalyzing the liquid phase hydrogenolysis of glycerol to 1,2-propandiol (68% conversion after 16 h) and 90% selectivity with ethylene glycol, 1-propanol and 2-propanol as main by-products. The role of the support has been highlighted in terms of acidic properties. The medium strength of Lewis acid sites of TiO2 leads to the best performance in terms of activity, selectivity and stability of the catalytic system.

Selectivity Engineering in Synthesis of Thymol Using Sulfated ZrO2–TiO2

Selective synthesis of thymol (6-isopropyl-3-methylphenol), a perfumery chemical, is challenging and was studied in this work by a continuous vapor phase alkylation of m-cresol using isopropyl alcohol over different solid acids. A series of novel zirconia–titania mixed sulfated oxides were prepared by the hydrothermal method and tested for isopropylation of m-cresol to prepare thymol. A sulfated catalyst with 2:1 mol ratio for zirconia/titania showed the best conversion and selectivity for thymol in a continuous fixed bed vapor phase reactor. The catalyst is stable and active for a long period of time, up to 20 h (TOS). Isopropylation of m-cresol was carried out in a continuous fixed bed vapor phase reactor under N2 as a carrier gas, 6.72/h WHSV, and 1:3 mol ratio of m-cresol to IPA at 220 °C. Reaction mechanism and kinetic model were developed. The reaction is kinetically controlled having an activation energy of 8.27 kcal/mol.

Synthesis of ordered porous zirconia containing sulfate ions and evaluation of its surface acidic properties

The synthesis and characterization of sulfated ZrO2 with ordered pores as a solid acid catalyst were investigated. Ordered porous ZrO2 containing sulfate ions was synthesized by hydrolysis of zirconium n-propoxide in the presence of HCl, surfactant and (NH4)2SO4 dissolved in distilled water, when the SO4/Zr molar ratio was changed in the range of 0.8–1.4. BET surface area of sulfated ZrO2 thus synthesized was found to be 150–160 m2 g−1. The presence of sulfate ions in ZrO2 was confirmed by an appearance of IR band at ca. 1398 cm−1 in the IR spectra of sulfated ZrO2. Since two IR bands due to surface hydroxyl groups were still observed for sulfated ZrO2, the possibility that sulfate ions are highly dispersed on the surface of ordered porous ZrO2 was suggested. From the evaluation of surface acidity by NH3-TPD measurements, not only the amount of NH3 desorption but also the strength of acid sites related to NH3 desorption temperature were found to be increased with increasing the SO4/Zr ratio up to 1.2. On the other hand, FTIR spectroscopy following pyridine adsorption revealed that the maximum surface density of Bronsted acid sites was attained for sulfated ZrO2 with SO4/Zr ratio of 1.0. Sulfate species interacting strongly with nano-sized tetragonal ZrO2 was considered to be responsible for the creation of Bronsted acid sites. In accordance with the surface density of Bronsted acid sites, sulfated ZrO2 with SO4/Zr ratio of 1.0 showed the highest activity for the skeletal isomerization of 3,3-dimethylbut-1-ene, which predominantly occurs on Bronsted acid sites.

The influence of selected process parameters on the reactions of n-hexane isomerization and transesterification catalyzed by sulfated zirconia

In view of the recent (ever) increasing need for environmentally friendly fuels, the processes of n-alkane isomerization and triglyceride(s) transesterification have gained importance because they enable the reduction of emissions of various hazardous substances into the environment. In this paper, sulfated ZrO2 as a heterogeneous acid catalyst was used in model reactions of isomerization of n-hexane and transesterification of sunflower oil. The goal of this research was to determine the optimal process parameters for isomerization and transesterification reactions, since they can have a large influence on both ecological and economical validity of these processes when used on the industrial scale. For the transesterification process, the parameters investigated were: the catalyst loading and methanol to oil molar ratio whereas in the isomerization reaction, the optimal process temperature was determined. The catalyst loading was proven to increase the yield of transesterification, but only until the mass percentage of the catalyst reaches 10%. The optimum methanol to oil molar ratio was shown to be 60:1, as further increase of the methanol amount decreases the transesterification yield. The temperature of 325ºC was determined to be optimal for the reaction of n-hexane isomerization under the experimental conditions applied.

Carbon Dioxide Hydrogenation on Au Nanoparticles Supported on TiO2, ZrO2 and Sulfated ZrO2 Under Supercritical Conditions

Hydrogenation of CO2 into CO and CH4 was studied for the first time on Au and Au–Ni catalysts supported on ZrO2, TiO2 and sulfated ZrO2 under supercritical conditions. The extremely high selectivity to CO exceeding 96–98 % was found with a quite good stability of the catalytic activity. Surprisingly, almost no methanation reaction was observed, this reaction being typical for nickel-based catalysts.

Esterification of stearic acid with methanol over mesoporous ordered sulfated ZrO2–SiO2 mixed oxide aerogel catalyst

Aerogel sulfated ZrO2–SiO2 mixed oxide solid acid catalyst was prepared by sol–gel method followed by supercritical drying (SCD) in n-propanol solvent, which resulted into higher surface area (170 m2/g), pore volume (0.31 cm3/g) and pore diameter (7.2 nm) having ordered mesoporous structure as well as more number of Bronsted and Lewis acid sites available on larger surface area. The catalyst exhibited 91 % yield of methyl stearate at 60 °C in 7 h, which increased from 71 to 91 % with an increase in the Zr to Si ratio from 1:2 to 2:1 due to increase in acid site concentration. The reaction followed pseudo-first order kinetics under the optimized reaction conditions with a reaction rate of 1.15 mmol h−1, rate constant of 2.7 × 10−1 h−1 and turn over frequency of 9.68 h−1. The catalyst displayed higher activity (91 %) compared to ion exchange resins (44–68 %), Nafion (58 %), acid clay (61 %) and pure sulfated zirconia (78 %), and was slightly lower as compared to H2SO4 (97 %). The study clearly reveals the improved structural, textural and acidic properties of ZrO2–SiO2 mixed oxide aerogel prepared via SCD technique.