Sulfated Catalysts Research Articles

Silver sulfate catalyst for soot oxidation with high resistance to sulfur poisoning

This study investigates the soot oxidation activity and mechanism of an Al2O3-supported Ag2SO4 catalyst with novel active species. The Ag2SO4/Al2O3 catalyst exhibits higher soot oxidation activity under loose contact conditions compared to Ag/Al2O3 and Ag/CeO2 catalysts. Moreover, it is hardly affected by sulfur poisoning and maintains its high activity after sulfur poisoning treatment. High-temperature X-ray diffraction measurements suggest that a part of Ag2SO4 on the Al2O3 support melts and creates contact between the Ag2SO4 and soot at temperatures over 400 °C, resulting in higher soot oxidation activity even under loose contact conditions. The soot oxidation mechanism over the Ag2SO4/Al2O3 catalyst is probed by oxygen isotope exchange analysis and operando X-ray absorption fine structure measurements, which reveal that the oxygen chemically bound in Ag2SO4 is utilized for soot oxidation. In particular, the above oxidation features a reversible redox cycle comprising partial reduction of Ag2SO4 to metallic Ag that is further re-oxidized to Ag2SO4 by the gas-phase oxygen.

Mechanism and Performance of the SCR of NO with NH3 over Sulfated Sintered Ore Catalyst

A sulfated sintered ore catalyst (SSOC) was prepared to improve the denitration performance of the sintered ore catalyst (SOC). The catalysts were characterized by X-ray Fluorescence Spectrometry (XRF), Brunauer–Emmett–Teller (BET) analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFTS) to understand the NH3-selective catalytic reduction (SCR) reaction mechanism. Moreover, the denitration performance and stability of SSOC were also investigated. The experimental results indicated that there were more Brønsted acid sites at the surface of SSOC after the treatment by sulfuric acid, which lead to the enhancement of the adsorption capacity of NH3 and NO. Meanwhile, Lewis acid sites were also observed at the SSOC surface. The reaction between −NH2, NH 4 + and NO (E-R mechanism) and the reaction of the coordinated ammonia with the adsorbed NO2 (L-H mechanism) were attributed to NOx reduction. The maximum denitration efficiency over the SSOC, which was about 92%, occurred at 300 °C, with a 1.0 NH3/NO ratio, and 5000 h−1 gas hourly space velocity (GHSV).

Sulfation effect of Ce/TiO2 catalyst for the selective catalytic reduction of NO x with NH3: mechanism and kinetic studies.

Ceria-based catalysts are competitive substitutes for the commercial SCR catalysts due to their high SCR activity and excellent redox performance. For a better understanding of the SO2 poisoning mechanism over ceria-based catalysts, the sulfation effect of the Ce/TiO2 catalyst on the SCR activity over a wide reaction temperature range was systematically studied via comprehensive characterizations, in situ DRIFT studies and kinetic studies. The results demonstrated that the NO conversion at 150 °C is significantly inhibited by the formation of cerium sulfites/sulfates due to the inhibited redox properties and excessive adsorption of NH3, which restrict the dissociation of NH3 to NH2, resulting in a much lower reaction rate of E–R reaction over the sulfated Ce/TiO2 catalyst. With the increase in the reaction temperature, the reaction rate of the E–R reaction significantly increased due to the improved redox properties and weakened adsorption of NH3. Moreover, the rate of the C–O reaction over the sulfated Ce/TiO2 catalysts is obviously lower than that of the fresh Ce/TiO2 catalyst. The promotion of NO conversion over the sulfated catalyst at 330 °C is attributed to both the increase in the reaction rate of E–R reaction and the inhibition of the C–O reaction.

Rapid and Efficient N-tert-butoxy carbonylation of Amines Catalyzed by Sulfated Tin Oxide Under Solvent-free Condition

A straightforward, rapid, and efficient protocol for the N-tert -butoxy carbonyl (N-Boc) protection of amines (aromatic, aliphatic) using sulfated tin oxide catalyst is illustrated. N -Boc protection of various amines was carried out with (Boc) 2 O using sulfated tin oxide as a catalyst at room temperature under solvent-free conditions. Rapid reaction times, ease of handling, cleaner reactions, easy work-up, reusable catalyst, and excellent isolated yields are the striking features of this methodology which can be considered to be one of the better methods for the protection of amines and alcohols. DOI: http://dx.doi.org/10.17807/orbital.v10i7.1155

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

Designing SO2-resistant cerium-based catalyst by modifying with Fe2O3 for the selective catalytic reduction of NO with NH3

In this study, CeO2-Nb2O5 and CeO2-Fe2O3-Nb2O5 mixed oxides used for the selective catalytic reduction of NO with NH3 (SCR) were prepared and the performance of these two samples was investigated. Given the modification of Fe2O3, catalyst sulfur resistance was significantly improved with the SCR activity remaining almost unchanged. For CeO2-Nb2O5 sample, SO2 reacted with the main redox sites, CeO2, to form inactive species, Ce2(SO4)3. By contrast, SO2 preferentially interacted with Fe2O3, which left surface cerium oxygen species preserved for CeO2-Fe2O3-Nb2O5 catalyst and enabled this sample with an enhanced SO2-resistant ability. At the same time, SO42− on the Fe2O3-added catalyst exhibited a lower stability. It seemed that CeO2-Fe2O3-Nb2O5 sample might be easily recycled via H2 regeneration at a relatively low temperature point and be a potential catalyst for the applications in the SCR systems.

Preparation of hierarchical HZSM-5 based sulfated zirconium solid acid catalyst for catalytic upgrading of pyrolysis vapors from lignite pyrolysis

H5 was developed to mesoporous system via alkali treatment, and sulfated zirconia (SZr) modified hierarchical HZSM-5 (AT0.2/H5) catalysts (named AT0.2/SZxH5) were successfully prepared by a series of post-treated method followed by Zr(NO3)4·5H2O and H2SO4 as active component. The innovative approach really enhanced acidity of AT0.2/H5 support, which results from the interaction of the sulfate groups attached to zirconia that doped on MFI framework with silanol groups. Adding active component can not only compensate for the loss of acid sites caused by NaOH treatment, but also re-develop more active sites owing to the formation of SZr. Meanwhile, NH3-TPD showed higher strong acid sites and weak acid sites in AT0.2/SZ6:1H5 than other prepared catalysts. The catalytic activity in converting lignite pyrolysis volatiles to light aromatics, including benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN), correlates well with the enhanced acidity. Compared with H5, the yield of light aromatics increased significantly from 15.2 to 19.3 mg/g over AT0.2/SZ6:1H5 at 600 °C. According to the characterization of N2 adsorption–desorption, SEM, and XRD, both the S species as SO42− and Z species as ZrO2 improved the textural properties of the support itself. Besides, the molar ratio of S/Zr was in direct proportion to the yield of BTEXN in a certain range, and 6:1 exhibited the optimal catalytic performance. The prepared solid acid catalyst provides a promising strategy to directional prepare light aromatics during lignite catalytic pyrolysis.

Catalytic oxidative cracking of n-propane over nanosized gold supported La2O3 catalysts

Nanosized gold deposited bare and sulfated La2O3 samples were synthesized and utilized for catalytic oxidative cracking of n-propane. Bare La2O3 showed only 10% conversion with 15% olefin selectivity, however significant enhancement in the conversion of n-propane was observed when La2O3 support was deposited with 0.2 wt% gold (25% conversion and 39% olefin selectivity) at 550 °C. Further improvement in conversion (46%) and in 53% selectivity was observed with gold supported 10 wt% SO42−/La2O3 catalyst. Gold supported sulfated La2O3 catalyst showed stable activity even after 20 h and the catalysts are resilient to formation of the coke. Presence of partially oxidized gold species and sulfate ions resulted enhancement in Lewis and Brönsted acidity of the catalysts. Homogeneous dispersion of gold nanoparticles and presence of metal-sulfate interactive species was observed in case of gold supported sulfated La2O3 catalyst as evidenced by TEM, CO chemisorption and H2-TPR analyses. The enhancement of catalytic activity could be attributed to small particle size, balanced Lewis and Brönsted acid sites and high dispersion of gold nanoparticles, surface area and oxygen mobility of the catalysts.

A Kinetic Investigation of Triacetin Methanolysis and Assessment of the Stability of a Sulfated Zirconium Oxide Catalyst

AbstractIn this work, the activity and stability of a sulfated zirconium catalyst in transesterification reactions of triacetin, a model molecule, were investigated. This catalyst has Lewis and Brønsted acid sites and has shown to be highly active in reactions converting triacetin into methyl esters. This catalyst was synthesized using the impregnation method, and systematically characterized using the techniques of x‐rays diffraction (XRD), scanning electron microscopy, Fourier transform‐infrared spectroscopy (FT‐IR), Brunauer, Emmett, and Teller, and thermal gravimetry analysis (TGA). Kinetic studies were carried out to determine the activation energy as well as the reaction order. The effects of the main reaction parameters, such as temperature, the molar ratio, and the catalyst content, were evaluated. The reuse and possible leaching of the catalyst were also investigated. The highest efficiency (ca. 99% of methyl esters) was achieved in the sulfated zirconium oxide‐catalyzed transesterification reaction.

Esterification of Levulinic Acid to Levulinate Esters in the Presence of Sulfated Silica Catalyst

Levulinic acid (LA) is one of biomass derived building block chemicals with various applications. Catalytic esterification of LA with alkyl alcohol produces levulinate ester which can be applied as fragrance, flavouring agents, as well as fuel additives. In this study, a series of sulfated silica (SiO2) catalyst was prepared by modification of SiO2 with sulfuric acid (H2SO4) at different concentrations; 0.5 M to 5 M H2SO4. The catalysts were characterized, and tested for esterification of LA with ethanol to ethyl levulinate (EL). The effect of various reaction parameters including reaction time, catalyst loading and molar ratio of LA to ethanol on esterification of LA to EL were inspected. The catalyst with high concentration of acid sites seemed suitable for LA esterification to EL. Among the sulfated SiO2 catalysts tested (0.5 M-SiO2, 1 M-SiO2, 3 M-SiO2 and 5 M-SiO2), 3 M-SiO2 exhibited the highest performance with the optimum EL yield of 54% for reaction conducted at reflux temperature for 4 h, 30% 3 M-SiO2 loading and LA to ethanol molar ratio of 1:20. Besides, the reusability of 3 M-SiO2 catalyst for LA esterification with ethanol was examined for five cycles. Esterification of LA with methanol and 1-butanol were also carried out for methyl levulinate (ML) and butyl levulinate (BL) productions with 69% and 40% of ML and BL yields, respectively. This study demonstrates the potential of sulfated SiO2 catalyst for levulinate ester production from LA at mild process condition.

Esterification of high acidity vegetable oil catalyzed by tin-based catalysts with different sulfate contents: contribution of homogeneous catalysis

Biodiesel production costs can be significantly reduced by using nonrefined feedstock. Sulfated solid catalysts have been proposed for producing biodiesel from acid oils by esterification reactions. Nevertheless, leaching of sulfate species to the reaction medium may occur, but often it is not considered. In this article, a commercial tin sulfate (SnSO4) was used as a catalyst for the esterification of a feedstock with high content of free fatty acid in order to assess the contribution of the homogeneous catalysis in different situations. SnSO4 was calcined at different temperatures (300, 400, 500 and 700 °C) and converted into SnO2 after calcination at temperatures higher than 300 °C. Homogeneous catalysis seems possible to occur with all of the catalysts, but it was clearly observed for the uncalcined catalyst (SnSO4) and for that calcined at 300 °C (SnSO4(300)). For these catalysts, an important leaching of the sulfate species was confirmed. Higher conversions were obtained with the uncalcined SnSO4. Reactions at the same conditions using sulfuric acid as catalyst at concentrations of 0.1% were performed and confirmed conversions higher than 80%. Heterogeneous catalysis plays a significant role only with the catalyst that present the highest specific surface areas and acidity (SnSO4(400)). As some small amount of sulfate species is retained in the structure or surface of the calcined catalysts (even after calcination at 700 °C), we cannot exclude the possibility that these species are also leached during reaction. Thus, a possible contamination of biodiesel through the use of sulfated catalysts cannot be ruled out.

Influence of calcination temperature on catalytic, acid and textural properties of SO42−/La2O3/HZSM-5 type catalysts for biodiesel production by esterification

In this study, the efficiency of catalysts based on La2O3/SO42− supported on HZSM-5 zeolites was evaluated for the biodiesel production by esterification. The effect of a prior dealumination of the zeolite on the prepared catalysts properties was analyzed, as well as the influence of the calcination temperature. These materials were characterized by TGA, XRD, N2 adsorption/desorption, FTIR, and FTIR with adsorption of probe molecules (pyridine and collidine) for the identification and quantification of acid sites. Model reaction of double bond position isomerization of 1-butene was also performed, in order to evaluate the acidity of the new catalysts produced. These solids were tested in the esterification reaction of oleic acid in presence of methanol and the influence of the molar ratio between the reactants was evaluated. The results indicate that HZSM-5 modified with La2O3/SO42− can be an efficient catalyst for the esterification reaction. Whatever the reactants molar ratio used, the sulfated catalysts were more efficient than the starting zeolite in the esterification of oleic acid. The dealumination of the zeolite prior to the impregnation with SO42−/La2O3 leads to materials with improved properties. Moreover, low temperature calcination (350 °C) was revealed to also produce catalysts with more interesting properties. The enhancement of the external surface properties (acidity and area) was the main parameter influencing the activity of the catalysts for the considered reaction.

Shape dependence and sulfate promotion of CeO2 for selective catalytic reduction of NOx with NH3

Thermally stable CeO2 cubes and nanospheres were synthesized and modified by sulfation treatment. Non-sulfated CeO2 cubes and nanospheres did not exhibit good catalytic performance for selective catalytic reduction of NOx with NH3 (NH3-SCR), but mainly contributed towards an undesired side reaction of NH3 oxidation above 350 °C. Based on the structural, morphological and physicochemical characterization, it was observed that CeO2 nanospheres comprising small crystallites could easily release active oxygen species, which resulted in strong NH3 oxidation. However, sulfation treatment greatly improved the catalytic performance of NH3-SCR on both CeO2 cubes and nanospheres. Sulfated CeO2 catalysts did not contribute to significant NH3 oxidation due to the inhibited reducibility of Ce4+ coordinated with the surface sulfates. The adsorbed ammonia could be activated on Brønsted acid sites generated by the formation of surface Ce2(SO4)3 species, while gaseous NOx could be activated on separate surface sites of Ce4+. The presence of separate reaction sites for NH3 and NOx is believed to be important for the improved catalytic performance of SCR reaction. Sulfated CeO2 cubes outperformed sulfated CeO2 nanospheres in the entire test temperature window (200–500 °C). The improved performance of sulfated CeO2 cubes appears to be related to surfaces with abundant Brønsted acid sites and relatively weak reducibility of Ce4+. These fundamental findings contribute to a better mechanistic understanding needed for designing efficient CeO2-based NOx reduction catalysts in the future.

Synthesis of quinazolinones and benzazoles utilizing recyclable sulfated metal-organic framework-808 catalyst in glycerol as green solvent

Zirconium-based metal-organic framework MOF-808 was synthesized, and sulfated with aqueous sulfuric acid. Sulfated MOF-808 was utilized as a recyclable heterogeneous catalyst for the synthesis of quinazolinones from β-ketoesters and benzamides, and for the synthesis of benzimidazoles from β-ketoesters and o-phenylenediamines in glycerol as a green solvent. The sulfated MOF-808 catalyst was more active than many heterogeneous and homogeneous catalysts. The combination of the sulfated MOF-808 and glycerol was also effective for the reaction of o-aminothiophenols with β-diketones or cyclic β-diketones to produce benzothiazoles. To our best knowledge, MOF-based catalysts were not previously utilized as heterogeneous catalyst in glycerol as green solvent.

Nature Identification of Cu Active Sites in Sulfur-Fouled Cu/SAPO-34 Regeneration

In order to probe the nature of regeneraion on the sulfated Cu/SAPO-34 selective catalytic reduction catalysts, CHA structure, copper species, and NOx conversion were investigated. A sulfated Cu/SAPO-34 catalyst was treated at different temperatures and times. The ammonia-sulfate species was removed at 500 °C, and copper sulfate was completely decompose at 750 °C. The NOx conversion of sulfated catalyst gradually recovers with the degree of regeneration increasing. XRD and ex situ DRIFTs results show that thermal treatment presents no effect on the framework structure of Cu/SAPO-34. The TPR and EPR results suggest that thermal treatment has an influence on the number of isolated Cu2+ and CuO instead of coordination environment and redox ability. However, the apparent activation energy of fresh, sulfated, and regenerated catalysts for SCR reaction remains the same, and turnover frequencies are also identical. The study reveals that the activity recovery is attributed to the increased number of active sites...

Three-component, solvent-free synthesis of Betti base catalyzed by sulfated polyborate

In this work, efficient, mild, and eco-friendly procedure of 1-aminoalkyl-2-phenol/Betti base from one-pot three-component condensations of aldehyde, phenol, and morpholine in the presence of sulfated polyborate catalyst, under a solvent-free condition at 100 °C, is described. The key advantages of the present method are short reaction time, high yields, aqueous work-up procedure, low cost, stable, reusable catalyst, and solvent-free reaction conditions.

Improved Biogas Generation from Biomethanated Distillery Wastewater by Pretreatment with Catalytic Wet Air Oxidation

Catalytic wet air oxidation (CWAO) is a prospective method for the treatment of distillery effluents. In this work, the biodegradability of biomethanated distillery spent wash (BOD5=8100 and COD=40000 mg/L) was improved by oxidation over ferrous sulfate catalyst. The homogeneous CWAO process was optimized by investigating the effects of reaction variables such as temperature (150-225 0C), oxygen partial pressure (0.69-2.07 MPa) and catalyst loading (16-48 mg/L). After oxidation at T=175 0C for 1 h, adsorption over activated carbon (loading 5%) was performed at ambient temperature. As a result, 73% reduction in COD and substantial rise (from 0.2 to 0.45) in the BOD5/COD ratio was observed. This ratio further rose to 0.52, when anaerobic digestion was performed using 1% acclimatized biomass. For every m3 of wastewater, 1.1 Nm3 of biogas was formed (methane 69%). After a final polishing step by aerobic treatment, BOD5/COD was 0.58 and 91% COD was destroyed. Clearly, this work has provided a useful solution t...

A Sulfated Polyborate Catalyst for the Synthesis of 1,5-Benzodiazepines

A Sulfated Polyborate Catalyst for the Synthesis of 1,5-Benzodiazepines

Simple and efficient conversion of cellulose to γ-valerolactone through an integrated alcoholysis/transfer hydrogenation system using Ru and aluminium sulfate catalysts

The conversion of cellulose to GVL was achieved through a one-pot reaction by integrating the alcoholysis and transfer hydrogen processes under microwave condition.

Degradation reaction of Diazo reactive black 5 dye with copper (II) sulfate catalyst in thermolysis treatment.

The theme of present research demonstrates performance of copper (II) sulfate (CuSO4) as catalyst in thermolysis process to treat reactive black 5 (RB 5) dye. During thermolysis without presence of catalyst, heat was converted to thermal energy to break the enthalpy of chemical structure bonding and only 31.62% of color removal. With CuSO4 support as auxiliary agent, the thermally cleaved molecular structure was further destabilized and reacted with CuSO4. Copper ions functioned to delocalize the coordination of π of the lone paired electron in azo bond, C=C bond of the sp2 carbon to form C-C of the sp3 amorphous carbon in benzene and naphthalene. Further, the radicals of unpaired electrons were stabilized and RB 5 was thermally decomposed to methyl group. Zeta potential measurement was carried out to analyze the mechanism of RB 5 degradation and measurement at 0mV verified the critical chemical concentration (CCC) (0.7g/L copper (II) sulfate), as the maximum 92.30% color removal. The presence of copper (II) sulfate catalyst has remarkably increase the RB 5 dye degradation as the degradation rate constant without catalyst, k1 is 6.5224 whereas the degradation rate constant with catalyst, k2 is 25.6810. This revealed the correlation of conversion of thermal energy from heat to break the chemical bond strength, subsequent fragmentation of RB 5 dye molecular mediated by copper (II) sulfate catalyst. The novel framework on thermolysis degradation of molecular structure of RB 5 with respect to the bond enthalpy and interfacial intermediates decomposition with catalyst reaction were determined.