Sulfated Catalysts Research Articles

Effect of vanadium on the behaviour of unsulfated and sulfated WTi-pillared clay catalysts forthe SCR of NO with NH3

Effect of vanadium on the behaviour of unsulfated and sulfated WTi-pillared clay catalysts forthe SCR of NO with NH3

Selective conversion of cellulose to hexitols over bi-functional Ru-supported sulfated zirconia and silica-zirconia catalysts

We report a process of selective conversion of microcrystalline cellulose to hexitols over bi-functional Ru-supported sulfated zirconia and silica-zirconia catalysts. A 58.1% yield of hexitols and a 71.0% conversion of cellulose were achieved over Ru/SZSi(100:15)-773 catalyst at 443 K. The as-synthesized catalysts were characterized by X-ray diffraction (XRD), BET, thermogravimetric analysis and pyridine adsorption Fourier transform infrared spectroscopy (FTIR). XRD results indicated that the sulfated catalysts were pure tetragonal phase of ZrO2 when calcined at 773 K. Monoclinic zirconia appeared at the calcination temperature of 873 K, and the content of monoclinic phase increased with the elevating temperature. Compared with sulfated zirconia catalyst, sulfated silica-zirconia catalysts possessed a higher ratio of Bronsted to Lewis on the surface of catalysts, as shown from pyridine adsorption FTIR results. The reaction results indicated that the tetragonal zirconia, which is necessary for the formation of superacidity, was the active phase to cellulose conversion. The higher amounts of Bronsted acid sites can remarkably accelerate the cellulose depolymerization and promote side reactions that convert C5–C6 alcohols into the unknown soluble degradation products.

Solvent free synthesis of methyl palmitate over sulfated zirconia solid acid catalyst

Sulfated zirconia (SZr) solid acid catalyst, prepared by conventional precipitation technique was studied for esterification of palmitic acid with methanol to synthesize methyl palmitate. The catalyst exhibited 90% yield of methyl palmitate at 60°C over 6wt% catalyst. The yield was significantly higher under solvent-free conditions than using hexane as a solvent. The alkyl palmitate yield was decreased with an increase in the alkyl chain of alcohol from methanol to n-butanol. The reaction followed pseudo-first order kinetics under the optimized reaction conditions with a reaction rate of 0.61mmolh−1, rate constant of 12.13×10−3h−1 and turn over frequency of 0.088min−1.

Photocatalytic degradation of terephthalic acid on sulfated titania particles and identification of fluorescent intermediates

Terephthalic acid (TA) is toxic and known as an endocrine disruptor. In this paper, the photocatalytic degradation of TA using sulfated titanium dioxide SO42−/TiO2 photocatalysts was investigated. The photocatalysts were prepared by sol–gel method and characterized by XRD, SEM, BET, ICP/MS and spectroscopic methods. Their activities were compared with bare TiO2 and Degussa P25. The effects of catalyst sulfur content, the initial TA concentration and pre-treatment conditions (O2, N2 or non-pretreated) were studied. O2 functions were also explored. Since there had been no comprehensive study of fluorescent intermediates reported yet, we investigated the intermediates and discovered 5 new intermediates (4 fluorescent and 1 non-fluorescent) which were identified by gas chromatography–mass spectrometry (GC/MS) and fluorescence spectroscopy. These intermediates are complementary to the previously identified carboxylic acid intermediates and might provide new insights to the mechanism of photocatalytic degradation of TA. Since TA is widely used as a probing molecule for photocatalytically generated ·OH radicals, the ratios of fluorescent intermediates of TA degradation may provide new clues to the photocatalytic activity and mechanism. Based on the results obtained, the possible destruction pathway of TA is also proposed.

Highly efficient sulfated Zr-doped titanoniobate nanoplates for the alcoholysis of styrene epoxide at room temperature

Sulfated Zr-doped titanoniobate nanoplates were prepared and evaluated as a solid acid catalyst in the alcoholysis of styrene epoxide at room temperature. Compared with undoped and Zr-doped nanosheets, the resulting sulfated catalyst exhibited an excellent catalytic performance to afford corresponding β-alkoxyalcohols (99% yield with methanol as nucleophile in only 10min) due to the high dispersion of zirconia species on nanosheets, appropriate Lewis acid strength and amount from the strong interaction between zirconia and sulfate species, and greatly increased surface area arisen from the exfoliation and house-of-cards restacking of nanosheets. The corresponding catalytic mechanism was proposed and discussed. The obtained material may act as a promising catalyst in many acid catalyzed reactions.

Sulfated Zirconium Catalyst for Synthesis of Dialkylated Diphenylether Disulfonate Gemini Surfactants

AbstractDialkylated diphenylether disulfonate with different alkyl chain lengths (Cn‐DADS, n = 8, 10 and 12) has been synthesized by Friedel‐Crafts alkylation of olefins (C8, C10 and C12) and diphenyl oxide, followed by sulfonation and neutralization with fuming sulfuric acid. Sulfated zirconia solid acids were prepared and used to catalyze the alkylation reaction. The structure of sulfated zirconia solid acids was identified by infrared spectroscopy. The title compounds were confirmed by infrared spectroscopy and electrospray ionization‐mass spectrometry. Equilibrium surface tension measurements show that the critical micelle concentration (CMC) decreases with an increase in chain length, and the surface tension at CMC (γcmc) of C8‐DADS is the lowest. The minimum area per molecule (Amin) values of Cn‐DADS increase, while the surface excess concentration (Γmax) values decrease with the increase of the alkyl chain length. C10‐DADS has the highest pC20 and CMC/C20 among Cn‐DADS.

Visible-light-responsive sulfated vanadium-doped TS-1 with hollow structure: Enhanced photocatalytic activity in selective oxidation of cyclohexane

A series of visible-light-responsive hollow sulfated V-doped TS-1 photocatalysts with different dopant content has been prepared by impregnation and evaluated in the selective photooxidation of cyclohexane by molecular oxygen. The activity results have been correlated with structural, electronic, and surface examinations of the photocatalysts with the help of X-ray diffraction, N2 physisorption, transmission electron microscopy, and Raman, XPS, infrared, and UV–visible spectroscopy. Irrespective of the reaction, a photocatalytic efficiency enhancement of valuable products (alcohols and ketones) with respect to V-doped titania (P25) references and V-doped and sulfated TS-1 catalysts was observed for hollow sulfated V-doped samples with the TiO4 species (tetrahedral Ti4+). This is likely linked with an effective narrowing of the band gap and results from a cooperative V, S effect on the structural properties of the TiO4 network inducing isolated energy levels near the conduction and valence bands. The simultaneous presence of V, S in the TS-1 also promotes the process with higher efficiency (TOF=2.37h−1, based on the molar amount of V sites) and chemoselectivity (cyclohexanone/cyclohexanol molar ratio=3.46) than in the homogeneous phase. Extensive computational modeling, together with the OVO4Si and OVO4Ti bridging sites on TS-1, was performed to show that OV and O4Ti (oxygen vacancy) in OVO4Ti bridging sites are the main active sites for the selective photooxidation reactions, and this is compatible with experimental observations for varying reaction conditions.

Lignin conversion in supercritical ethanol in the presence of solid acid catalysts

The effects of sulfated ZrO2 and ZrO2-Al2O3 catalysts and acidic zeolite catalysts with various Si/Al ratios on the thermal conversion of alkali lignin in supercritical ethanol at 300–400°C and on the composition of the resulting products have been investigated. All of the catalysts enhance lignin conversion into liquid products. The strongest effect with the catalysts based on sulfated ZrO2 is attained at 400°C; with the zeolites, at 350°C. The catalysts diminish the concentration of phenol and its derivatives and increase the concentration of ethers (mainly the 1,1-diethoxyethane concentration) in the liquid products. The zeolite catalysts are preferable, since the reaction over the ZrO2-containing catalysts produces gaseous compounds in higher yields. The maximum lignin conversion and a high yield of low-boiling liquid products are achieved at 350°C with the zeolite catalyst with Si/Al = 30, which contains a high concentration of acid sites that are stable at elevated temperatures. The most abundant phenolic liquid products of lignin conversion over the zeolite catalysts at 350°C are methoxyphenols and their methylated and ethylated derivatives.

Hydrothermally Stable, Conformal, Sulfated Zirconia Monolayer Catalysts for Glucose Conversion to 5-HMF

The grafting and sulfation of zirconia conformal monolayers on SBA-15 to create mesoporous catalysts of tunable solid acid/base character is reported. Conformal zirconia and sulfated zirconia (SZ) materials exhibit both Bronsted and Lewis acidity, with the Bronsted/Lewis acid ratio increasing with film thickness and sulfate content. Grafted zirconia films also exhibit amphoteric character, whose Bronsted/Lewis acid site ratio increases with sulfate loading at the expense of base sites. Bilayer ZrO2/SBA-15 affords an ordered mesoporous material with a high acid site loading upon sulfation and excellent hydrothermal stability. Catalytic performance of SZ/SBA-15 was explored in the aqueous phase conversion of glucose to 5-HMF, delivering a 3-fold enhancement in 5-HMF productivity over nonporous SZ counterparts. The coexistence of accessible solid basic/Lewis acid and Bronsted acid sites in grafted SZ/SBA-15 promotes the respective isomerization of glucose to fructose and dehydration of reactively formed fructose to the desired 5-HMF platform chemical.

Impact of sulfation and desulfation on NOx reduction using Cu-chabazite SCR catalysts

This bench reactor study investigates the impact of gaseous sulfur on the NOx reduction activity of Cu-chabazite SCR (Cu-CHA) catalysts at SO2 concentrations representative of marine diesel engine exhaust. After 2h of 500ppm SO2 exposure at 250 and 400°C in the simulated diesel exhaust gases, the NOx reduction activity of the sulfated Cu-CHA SCR catalysts is severely degraded at evaluation temperatures below 250°C; however, above 250°C the impact of sulfur exposure is minimal. EPMA shows that sulfur is located throughout the washcoat and along the entire length of the sulfated samples. Interestingly, BET measurements reveal that the sulfated samples have a 20% decrease in surface area. Furthermore, the sulfated samples show a decrease in NOx/nitrate absorption during NO exposure in a DRIFTS reactor which suggests that Cu sites in the catalyst are blocked by the presence of sulfur. SO2 exposure also results in an increase in NH3 storage capacity, possibly due to the formation of ammonium sulfate species in the sulfated samples. In all cases, lean thermal treatments as low as 500°C reverse the effects of sulfur exposure and restore the NOx reduction activity of the Cu-CHA catalyst to that of the fresh condition.

Selective Monolaurin Synthesis through Esterification of Glycerol Using Sulfated Zirconia-Loaded SBA-15 Catalyst

The selective conversion of lauric acid to glycerol monolaurin over sulfated zirconia SBA prepared under various conditions was investigated in this study. The structural properties of the prepared catalysts were characterized using different characterization techniques. Sulfated zirconia was successfully incorporated with improved properties, such as larger mesopore surface area; the mesoporous structure was preserved as well. The highest yield of 79.1% was obtained during reaction over SZSBA-15 catalyst with 16 wt.% zirconium oxychloride loading and 3 h of reflux time. About 83.4% selectivity toward monolaurin was achieved at a high conversion of lauric acid (94.9%), a lauric acid-to-glycerol molar ratio of 4.0, within 6 h, and at 160°C. Product distribution was successfully elucidated. High selectivity to monolaurin was influenced by molecular sieving effects.

Fructose Dehydration to 5-Hydroxymethylfurfural over Sulfated TiO2–SiO2, Ti-SBA-15, ZrO2, SiO2, and Activated Carbon Catalysts

Different sulfated catalysts including SO4/TiO2–SiO2, SO4/Ti-SBA-15, SO4/ZrO2, SO4/AC, and SO4/SiO2 were tested in fructose dehydration to 5-hydroxymethylfurfural (HMF). Reactions were carried out in dimethyl sulfoxide (DMSO) at 110 °C. Characterization results indicated that no sulfur leaching was observed from SO4/ZrO2, SO4/TiO2–SiO2, and SO4/Ti-SBA-15 catalysts in the reaction tests. The SO4/TiO2–SiO2 catalyst had a high amount of strong acid sites and the highest amount of Bronsted sites. The highest selectivity to HMF at high conversion, that is, 89% selectivity at 77% fructose conversion was obtained over this catalyst. It preserved its activity after four times reuse.

A facile designed highly moderate craspedia flowerlike sulphated Bi2O3-fly ash catalyst: Green synthetic strategy for (6H-pyrido[3,2-b]carbazol-4-yl)aniline derivatives in water

The air pollutant fly ash was facile designed as a green catalyst and practical to organic synthesis. We have designed sulfated Bi2O3-fly ash catalyst (12wt%) and it was characterized by Fourier transform infrared (FT-IR), confocal Raman, Powder X-ray diffraction (XRD), Field emission electron microscopy (FE-SEM), elemental color mapping, energy-dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) techniques. The sulfated Bi2O3-fly ash was found an excellent catalytic application for the synthesis of (6H-pyrido[3,2-b]carbazol-4-yl)aniline derivatives in water has been described. The synthesized (6H-pyrido[3,2-b]carbazol-4-yl)aniline derivatives were confirmed by spectral techniques Fourier transform infrared (FT-IR), Nuclear magnetic resonance (NMR) and Liquid chromatography–mass spectrometry (LC–MS). The significant catalytic role of Bi–N interaction was readily form adduct, moreover Bi–O bond was favorable for hydrogen abstraction, dehydration and aromatization. Due to the strong potential, the precise reaction time and high yield have been achieved, which is realized from hot filtration test. The sulfated Bi2O3-fly ash catalyst could be reused for five successive run, the resulting in no appreciable change in the catalytic activity. The crystal phase and surface morphology of fifth run catalyst were examined by powder XRD, FE-SEM, EDS and TEM techniques, and the results revealed no changes in catalyst nature. The sulfated Bi2O3-fly ash catalyst has high efficiency, reusability, good catalytic activity, environmentally harmless and notable potential in industrial applications.

XANES and DRIFTS study of sulfated Sb/V/Ce/TiO2 catalysts for NH3-SCR

A study of structural and mechanistic investigation of the Sb/V/Ce/Ti catalysts sulfated at different temperatures was carried out by X-ray absorption near edge spectroscopy (XANES) and diffused reflectance infrared Fourier transformed spectroscopy (DRIFTS). The high temperature sulfated catalyst, especially Sb/V/Ce/Ti-S500 (sulfated at 500°C temperatures), exhibited superior NOx conversion at low temperatures (150–200°C) compared to Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S300 (sulfated at 400 and 300°C) catalysts. The Ce L3 edge XANES spectra of Sb/V/Ce/Ti-S500 catalyst showed the formation of Ce(III) dominant sulfate species, resulting in the enhancement of Lewis and Brønsted acid strength. The formation of Ce(III) sulfate species on Sb/V/Ce/Ti-S500 catalyst was clearly indicated by Ce M4,5 and S K edge XANES spectra peaks at 881.9eV attributed to Ce3+ oxidation state and 2481eV assigned to S6+ oxidation state of sulfate species. Furthermore, the in situ DRIFTS results revealed that the Lewis and Brønsted acid sites of Sb/V/Ce/Ti-S500 catalysts increased significantly, followed by Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S300. At 200°C, the reaction between the pre-adsorbed NH3 species with NO+O2 on sulfated catalysts exhibited the formation of mono-dentate, bi-dentate, bridging nitrates and NO2 species. Meanwhile, the subsequent formation of NO2 via NO oxidation was promoted on Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S500 catalysts, followed by surface interaction with adsorbed NH3 to produce N2 and H2O at low temperatures (<220°C).

Sulfated Iron Oxide: A Proficient Catalyst for Esterification of Butanoic Acid with Glycerol

Sulfated iron oxide catalysts, prepared by a simple and solvent free method, were studied in the esterification of butanoic acid with glycerol. The effect of the series of preparation parameters such as mixing time, sulfate loading, and calcination conditions, i.e., temperature and its duration, were explored. The catalyst containing 6 wt % sulfate loading with 40 min of mixing time, calcined at 500 °C for 7 h, performed optimally for the conversion of butanoic acid. The characterization of catalysts was carried out by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC)-thermogravimetric analysis (TGA), zeta potential, acidity measurements, and leaching tests. The performance of the catalyst has revealed that it is a low cost, stable, efficient heterogeneous catalyst for this reaction when compared with ion exchange resins and other heterogeneous catalys...

Esterification of palmitic acid with methanol over template-assisted mesoporous sulfated zirconia solid acid catalyst

The esterification of palmitic acid with methanol was studied over mesoporous sulfated zirconia (SZ) solid acid catalyst, prepared by using CTAB cationic surfactant as a template. The effect of various reaction parameters has been studied. The catalyst showed an excellent activity with 88–90% yield of methyl palmitate at 60°C after 5–7h. The reaction follows pseudo-first order kinetics under the reaction conditions studied with a reaction rate of 48.67mmolh−1g−1 and turnover frequency of 6.96h−1. It is noteworthy that SZ catalyst showed comparable activity to conventional Brönsted acids namely H2SO4 and p-TSA; as well as it exhibited higher activity than various other heterogeneous catalysts such as zeolites, ion-exchange resins and acid clay.

Sodium Sulfide: A Sustainable Solution for Unbalanced Redox Condensation Reaction between o-Nitroanilines and Alcohols Catalyzed by an Iron–Sulfur System

Unbalanced redox condensation reaction between o-nitroanilines and alcohols, leading to benzimidazole and quinoxaline heterocycles can be efficiently promoted and catalyzed by sodium sulfide (40 mol%) in combination with iron(III) chloride hexahydrate (1 mol%). Beside the role as a precursor for the iron–sulfur (Fe/S) catalyst formation, hydrated sodium sulfide was shown to be an excellent noncompetitive, multi-electron reducing agent.

Improved sulfur-resistant ability on CO oxidation of Pd/Ce0.75Zr0.25O2 over Pd/CeO2-TiO2 and Pd/CeO2

The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/CeO2-TiO2 and Pd/CeO2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), CO chemisorption, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and X-ray fluorescence (XRF). After 10 h SO2 sulfation, it was found that the decrement on CO oxidation catalytic activity was limited on Pd/Ce0.75Zr0.25O2 compared to Pd/CeO2-TiO2 and Pd/CeO2. It demonstrated that Pd/Ce0.75Zr0.25O2 was more sulfur resistant compared to the other two catalysts. After sulfur exposure, catalyst texture was not much influenced as shown by N2 adsorption and XRD, and surface Pd atoms were poisoned indicated by CO chemisorption results. Pd/Ce0.75Zr0.25O2 and Pd/CeO2-TiO2 exhibited less sulfur accumulation compared to Pd/CeO2 in the sulfation process. Furthermore, XPS results clarified that surface sulfur amount, especially surface sulfates amount on the sulfated catalysts was more crucial for the deactivation in sulfur containing environment.

CONDENSATION REACTION OF GLYCEROL AND CARBONYL COMPOUNDS: SYNTHESIS, CHARACTERIZATION, AND DERIVATIZATION FOR LIQUID CRYSTALS

Condensation reactions of glycerol with aldehydes and ketones were performed under thermal heating and microwave irradiation regimes. Homogeneous and heterogeneous catalysts were tested in both conditions. A silica sulfated (SiO2-SO3H) heterogeneous catalyst demonstrated the best performance relative to a selectivity of >95% in favor of 5-membered ketals. For acetals, preference in favor of 5-membered or 6-membered functional groups depends on the nature of the catalyst. Homogenous catalysts favor the more stable 6-membered acetals, whereas heterogeneous catalysts favor the less stable 5-membered acetals. However, the isomer ratios in the acetalization reaction are too low, and hence the reaction cannot be used in a synthetic plan for functional materials. Ketalization processes mediated by SiO2-SO3H show a high selectivity in favor of a 5-membered ring (1,3-dioxolane). The scope of condensation was tested with different ketones. A mechanism for heterogeneous catalysis related to the selectivity in the cyclization process is presented herein. Solketal, a commercial product, was also obtained by a condensation reaction of glycerol and propanone, and showed a high selectivity in favor of 1,3-dioxolane. It was transformed to potential allylic and chiral intermediates. A mesogenic core was connected to the organic framework of glycerol to produce a monomer liquid crystal material with a stable smectic-C mesophase.

Mechanochemical synthesis of TiO2/NiFe2O4 magnetic catalysts for operation under RF field

Composite NiFe2O4–TiO2 magnetic catalysts were prepared by mechanochemical synthesis from a mixture of titania supported nickel ferrite nanoparticles and P25 titania (Evonic). The former provides fast and efficient heating under radiofrequency field, while the latter serves as an active catalyst or catalyst support. The highest heating rate was observed over a catalyst prepared for a milling time of 30 min. The catalytic activity was measured over the sulfated composite catalysts in the condensation of aniline and 3-phenylbutyric acid in a stirred tank reactor and in a continuous RF heated flow reactor in the 140–170 °C range. The product yield of 47% was obtained over the sulfated P25 titania catalyst in the flow reactor.