Tin Oxide Catalysts Research Articles

Mesoporous tin oxide: An efficient catalyst with versatile applications in acid and oxidation catalysis

Mesoporous tin oxide was prepared by template assisted and template-free methods. As-prepared materials were calcined at various temperatures to generate different nature (Brønsted and Lewis), amount and strength of acidic sites. The physico-chemical properties of the catalysts were studied by XRD, N2 sorption, pyridine-FTIR, NH3-TPD, DRS UV-vis, TGA, SEM, TEM, 1H MAS and 119Sn MAS NMR analyses. The catalytic behavior of mesoporous tin oxide catalysts was evaluated for acetalization and ketalization of glycerol with benzaldehyde and acetone respectively under solvent free conditions. The catalytic performance of mesoporous tin oxide was compared with that of other conventional solid acid catalysts namely H-ZSM-5, H-mordenite, H-beta, Al-MCM-41, Al-SBA-15 and Al-TUD-1. The efficiency of mesoporous tin oxide was also tested for cyclohexene epoxidation reaction. The catalyst prepared by template assisted method showed excellent catalytic performance compared to other catalysts due the difference in nature and amount of acidic sites in the catalyst. Meso-SnO2-T-350 was stable and reusable catalyst for four cycles without any appreciable loss in activity, and therefore it offers a good catalyst for potentially wide applications.

Understanding Electrochemical Reduction of CO2 Using Quantum Chemistry Modeling

Electrochemical reduction of CO2 into usable hydrocarbons by multiple proton and electron transfers is hindered by slow kinetics and unfavorable thermodynamics. Experiments have reported a wide range of compounds from organic molecules to metal oxides to be suitable homogenous catalysts that can facilitate the above multi-step reaction. Quantum chemical calculations and certain thermodynamic descriptors help in identifying electrochemical conditions at which catalysts participate in energetically efficient proton and electron transfers [1]. We discuss how Pourbaix diagrams can be useful descriptors to identify several organic molecules and inorganic compounds that electrochemically catalyze the conversion of CO2 [2-4]. We present our latest results on modeling CO2 electroreduction on tin oxide catalysts and our prediction of new dopants that result in lower overpotentials than undoped tin oxide [5].

Effect of Metals Compatibility on Fluorine-Doped Tin Oxide Catalyst for Glycerol Conversion to 1,2-Propanediol

The effect of metals on support material fluorine-doped tin oxide (FTO), were studied. A series of metals such as ruthenium (Ru), osmium (Os), palladium (Pd), and copper (Cu) on FTO support were prepared by a simple wet mixture method, and attempted as a heterogeneous catalyst to enhance the hydrogenolysis of glycerol converted to 1,2-propanediol (1,2-PDO). The physicochemical properties of the catalysts were characterized by XRD, XPS, BET, FESEM, TEM, TPR, and TPD techniques. In particular, the catalyst of Ru-FTO was recorded as a good catalyst with an optimum glycerol conversion of 100% and 1,2-PDO selectivity of 94% respectively. It was suggesting that the acid an basic properties of the catalyst could achieved the C-O and C-H bond dissociation by formation of different intermediates of acetol and acetaldehyde to become 1,2-PDO. Despite that, some reaction parameters were evaluated and optimized reaction condition were established

Nature of active tin species and promoting effect of nickle in silica supported tin oxide for dehydrogenation of propane

Different with Wang et. al.’s study, we found that polymeric Si–O–Sn2+ rather than Ni-Sn alloy and metallic Sn are active species in silica-supported tin oxide catalysts for dehydrogenation of propane. The results showed that high surface area of mesoporous silica brought about high dispersion of tin oxide species, as a result, catalytic activity and stability were both improved. DRUV–vis, XPS, TPR and XRD studies of fresh and reduced catalysts indicated that the deactivation was related to the reduction of active species rather than the coke formation since active tin species cannot maintain its oxidation state at reaction conditions (high temperature and reducing atmosphere). The formed Ni3Sn2 alloy after reduction just functioned as promoter which accelerated the desorption of H2 and regeneration of active site. A synergy effect between active tin species and Ni3Sn2 alloy were observed.

Conversion of d-glucose to 5-hydroxymethylfurfural using Al2O3-promoted sulphated tin oxide as catalyst

Innovative catalysts to convert biomass carbohydrates in high value products are of an immense interest for the chemical industry and biorefineries. In this study, modified tin oxide (SnO2) catalysts were synthesised and submitted to H2SO4 treatment (SO4−2/SnO2) and alumina doping (SO4−2/Al2O3-SnO2) using different calcination temperatures. The effect of these modifications on the catalyst performance were investigated by examining the catalysts properties and activity for the conversion of glucose to 5-hydroxymethylfurfural. The incorporation of alumina in the sulphated tin oxide catalyst and the use of low calcination temperatures increased the specific surface area and the acidity of the catalyst. This enhanced the chemo-selectivity of the conversion of glucose to 5-hydroxymethylfurfural. This catalyst was recovered after reaction by solvent washing and re-calcination; however, the recovery procedures were insufficient to avoid a decay of the catalyst performance during subsequent runs.

Fluorine-doped tin oxide catalyst for glycerol conversion to methanol in sub-critical water

In this study, a method for the catalytic conversion of glycerol to methanol in sub-critical water (subCW) is proposed. Glycerol conversion to methanol using the subCW method is a new attempt to the best of the authors’s knowledge and this process was compared with the conventional hydrogenolysis method. For the first time, fluorine-doped tin oxide (FTO) was applied as a novel heterogeneous catalyst for the conversion of glycerol to methanol. The sub-critical reaction was conducted under optimal and mild conditions at a reaction temperature of 300°C, reaction time of 30min, and at a low pressure sufficient to maintain the liquid phase. Initial feedstock (glycerol) concentration and catalyst amount of 20wt% and 0.01g respectively, were utilized and glycerol conversion and methanol selectivity were measured using gas chromatography-flame ion detector (GC-FID) analysis. Optimum glycerol conversion of ∼80% was achieved, with methanol as the major product with a selectivity of ∼100%. The subCW method can also be applied for extraction processes as well as biomass conversion by optimizing some parameters such as reaction time, catalyst amount, reaction temperatures, and catalyst cyclability.

Novel hierarchical SnO2 microsphere catalyst coated on gas diffusion electrode for enhancing energy efficiency of CO2 reduction to formate fuel

The conversion of carbon dioxide to value-added fuel using electrical energy generated intermittently from renewable energy sources is very promising in terms of energy usage reconciliation. The process converts greenhouse carbon dioxide gas to produce diverse attractive chemicals and fuels like methanol, formate, and other hydrocarbons. In this paper, the electroreduction of CO2 to formate in aqueous solution is performed by using novel hierarchical tin oxide microsphere (HMS-SnO2) particles deposited over gas diffusion layer electrode (HMS-SnO2/GDE). The experiment is carried out in a divided H-type two-compartment cell with a Nafion® membrane as the diaphragm separating the cathodic and anodic compartments. The HMS-SnO2 catalysts are synthesized by a facile hydrothermal self-assembled process using different ratios of ethanol to distilled water in the synthetic solution. Due to the outstanding catalytic activity and selectivity toward CO2 electroreduction, SnO2-86/GDE exhibits a high Faradaic efficiency of 62% toward formate formation at −1.7V vs. SHE (Standard Hydrogen Electrode). The electrode durability is also observed with a stable current density over 12h of continuous electrolysis operation. The superior performance is credited to the morphology- and size-controlled hierarchical structure, which may provide more active sites to accelerate the slow kinetics of CO2 reduction, leading to the improved energy efficiency. During electrolysis process, KHCO3 electrolyte is found to have some contribution to formate formation on the micro-structured tin oxide catalysts coated GDE electrode.

Cesium exchanged tungstophosphoric acid supported on tin oxide: An efficient solid acid catalyst for etherification of glycerol with tert-butanol to synthesize biofuel additives

Cesium exchanged tungstophosphoric acid (CsTPA) supported on tin oxide catalysts were prepared and their physio-chemical properties were derived from X-ray diffraction, FT-IR, laser Raman spectroscopy and temperature programmed desorption of NH3. The catalysts activity was evaluated for etherification of glycerol with tert-butanol. The characterization results of the catalysts revealed that the primary Keggin structure remained intact during the exchange of TPA protons with Cs+ ions. The activity results showed that etherification activity depended on the amount of the CsTPA over SnO2 and the catalyst with 20wt% CsTPA supported on SnO2 showed high catalytic activity with 90% glycerol conversion with 44% selectivity toward higher ethers. The activity of the catalyst depends on amount of surface acidic sites and dispersion amount of CsTPA over SnO2. The etherification reaction was carried at different reaction parameters and optimum reaction conditions were established. The catalysts were recyclable and showed constant activity up on reuse.

Indium Tin Oxide as Catalyst Support for PEM Fuel Cell: RDE and MEA Performance

High surface area indium tin oxide (ITO) catalyst support materials were synthesized by using co-precipitation method to get uniform and small particle size. Colloidal deposition was used to deposit platinum onto the ITO support. The ITO support demonstrated exceptional electrochemical stability in RDE tests with less than 10% double layer pseudo capacitance loss compared with a 270% change for Vulcan XC-72R carbon under the standard support stability protocol (start-stop). 40%Pt/ITO catalyst showed higher durability than the commercial Pt/C when tested using the support stability protocol. The ECSA change for 40%Pt/ITO was similar to 46%Pt/C (TKK) under catalyst stability protocol (load cycling) but it showed less than 4% ECSA change compared with 40% loss for commercial catalyst under support stability protocol. The baseline mass activities (RDE) for the two catalysts (Pt/ITO and Pt/C) were similar. However, the fuel cell performance in the MEA was very poor for 40%Pt/ITO catalyst and XPS and EDX techniques revealed the formation of indium hydroxide and support degradation upon fuel cell operation, though these modes were not evident upon testing in an RDE.

Understanding the surface and structural characteristics of tungsten oxide supported on tin oxide catalysts for the conversion of glycerol

Catalysts with varying WO3 content on SnO2 were prepared and characterized by X-ray diffraction, in situ Raman spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption of NH3. In situ Raman analysis reveals the presence isolated monomers and polymeric species of WO3. These catalysts were evaluated for the conversion of glycerol into value added chemicals. Etherification of glycerol with tertiary butanol and preparation of glycerol carbonate from glycerol and urea are studied over these catalysts. The catalytic activity results suggest that the glycerol conversion and selectivity depends on the morphology of WO3 which in turn is related to its content in the catalyst. The catalysts with 5 wt.% of WO3 on SnO2 resulted in high dispersion with larger number of strong acidic sites. The selectivity in the glycerol etherification is related to the nature of the catalyst and reaction time. These catalysts also exhibited high activity for synthesis of glycerol carbonate. The effect of various reaction parameters was studied to optimize the reaction conditions. The catalysts also exhibited consistent activity upon reuse. Tungsten oxide supported on tin oxide is a highly active catalyst for selective etherification of glycerol to mono tert-butyl glycerol ethers. The activity of the catalyst depends on the surface and structural characteristics which are related to the content of WO3 on SnO2.

Unprecedented Reductive Esterification of Carboxylic Acids under Hydrogen by Reusable Heterogeneous Platinum Catalysts

AbstractSupported metal catalysts have been tested for an unprecedented reductive dimerization of carboxylic acids to esters under 8 bar hydrogen in solvent‐free conditions. Among various metal‐loaded tin oxide catalysts, platinum‐loaded tin dioxide (Pt/SnO2) shows the highest ester yield for the reaction of dodecanoic acid. Among Pt catalysts on various supports, Lewis acidic oxides, especially SnO2, show high activity. The most active catalyst, 5 wt% Pt/SnO2 reduced at 100 °C, is effective for the reductive esterification of various carboxylic acids, and the catalyst is reusable for nine cycles, demonstrating the first successful example for the title reaction. Infrared (IR) studies of a model compound (formic acid) on some metal oxides indicate a strong Lewis acid‐base interaction between SnO2 and the carbonyl oxygen. For Pt/SnO2 catalysts with different Pt particle sizes, the activity increases with decreasing size of Pt metal. A cooperative catalysis of the Pt metal nanoparticles and the Sn4+ Lewis acid sites is proposed.magnified image

High-activity of Pd catalyst supported on antimony tin oxide for hydrogen peroxide electroreduction

Abstract Pd electrocatalysts supported on antimony tin oxide and Vulcan XC-72 were both synthesized via a modified sodium borohydride reduction method. The catalysts were characterized by means of powder X-ray diffraction and cyclic voltammetry. Linear sweep voltammetry, open circuit potential curves and chronoamperometry were employed to evaluate the activities of the catalysts. The results show the particle size of Pd in the Pd electrocatalysts supported on antimony tin oxide catalyst is about 2.5 nm, which is smaller than that of the Pd electrocatalysts supported on Vulcan XC-72 (about 6.3 nm), and the surface area of the Pd electrocatalysts supported on antimony tin oxide electrode is larger than that of the Pd electrocatalysts supported on Vulcan XC-72 electrode. The Pd catalyst supported on antimony tin oxide shows superior performance to the catalyst supported on Vulcan XC-72.

Efficient and selective conversion of fructose to 5-hydroxymethylfurfural over metal exchanged heteropoly tungstate supported on tin oxide catalysts

A series of Al exchanged heteropoly tungstate (AlTPA) supported on SnO2 catalysts were prepared and characterized by FT-Infrared, X-ray diffraction and temperature programmed desorption of ammonia. The catalysts were evaluated for dehydration of fructose to 5-hydroxymethylfurfural (5-HMF). The catalysts showed high activity for dehydration of fructose and the catalyst with 20 % AlTPA on SnO2 exhibited highest activity. The high activity of AlTPA catalysts related to the presence of Lewis acidic sites apart from Bronsted acidic sites generated due to presence of Al. The active catalyst was further treated at different temperature to understand the surface-structural variations and thereby their influence on fructose dehydration activity. High temperature calcinations of catalysts leads to destabilization of Keggin unit and resulted a decrease in acidity. The dehydration of fructose activity and selectivity towards 5-HMF product also depends on the reaction temperature, time and catalyst weight.

Mechanical properties and bioactivity of calcium silicate/poly(ethylene terephthalate-co-caprolactone) composites

Calcium silicate/poly(ethylene terephthalate-co-caprolactone) (CS/PET-co-PCL) composites were prepared via ring opening polymerisation (ROP) technique. The CS/PET-co-PCL composites were prepared by mixing 60 wt-% of CS, 40 wt-% of cyclics and dibutyl tinoxide catalyst (3 mol.-% with respect to cyclics). The cyclics consisted of the mixture of cyclic oligo(ethylene terephthalate) (C-OET) and ϵ-caprolactone (CPL) with varying molar ratio of C-OET/CPL, i.e. 7∶3, 8∶2 and 9∶1. The precomposites were then ring opening polymerised at 200°C for 24 h. The ROP-PET-co-PCL in the composites was present as a continuous phase impregnated with the CS particles. The 1H-NMR spectra of ROP-PET-co-PCL extracted from the CS/PET-co-PCL composites showed heterolinkage signals between PET and PCL at δ 4·4 and δ 4·6 ppm, indicating successful copolymerisation. When the PCL content increased, the ROP-PET-co-PCL changed in the copolymer structure from block to random structure. The presence of CS powders in the CS/PET-co-PCL composites resulted in high stiffness of the composites and inhibited heat dissipation during the dynamic mechanical analysis performed between −50 and 200°C. The compressive strengths of all the composites were in the range of 16–21 MPa. The higher the PET content, the stronger the CS/PET-co-PCL composites obtained. Composites containing 9∶1 of C-OET/CPL polymerised at 200°C possessed the highest compressive strengths of 21·3 MPa, falling in the range of cartilage bone, i.e. 14–59 MPa. Bioactivities of the CS/PET-co-PCL composites were studied by soaking in simulated body fluid for 7 days. All CS/PET-co-PCL composites could induce the formation of hydroxyapatite nanocrystals on the composite surfaces, indicating the bioactivity of the CS/PET-co-PCL composites.

Effect of Nitric Acid Concentration on Doping of Thin Film Single-walled Carbon Nanotubes for Electrode Application in Transparent, Flexible Dye Sensitized Solar Cells

ABSTRACTA simple method is proposed for the chemical modification of carbon nanotubes (CNT) thin film counter electrodes (CE) for the replacement of fluorine-doped tin oxide (FTO) and platinum catalyst (Pt) while retaining light transparency. In order to decrease the sheet resistance, CNT thin films underwent various concentrations (≤10 M) and durations of HNO3 treatment prior to cell fabrication, and the effect on thin film properties was analyzed. P-doping was observed, and the maximum change in work function was found to be +0.35 eV with 4 M HNO3. Optimum sheet resistance reduction (50%) and work function increment were achieved after 1 h treatment with 4 M HNO3. Changes in optical transmittances for all samples were negligible (± 5%). Pristine and HNO3 treated films on plastic substrates were tested as CE in flexible bifacial dye sensitized solar cells (DSSC). Most significant improvements in conversion efficiencies were obtained when CNT on plastic substrates were pretreated with 8 M HNO3 (from 1.18% to 1.40% under roomlight, from 0.19% to 0.26% under 1 Sun).

Preparation, characterization and catalytic activity of WO3 supported on sulfated tin oxide catalysts

Solid acid catalysts of 15wt.%SO4/SnO2 loaded with 5–45wt.%WO3 were prepared, calcined at 400–800°C, and then characterized by TG–DTA, XRD, FT-IR spectra and nitrogen adsorption techniques. The surface acidity was determined by potentiometric titration with n-butylamine in acetonitrile and FT-IR spectra of chemisorbed pyridine.The presence of sulfate ions together with WO3 hindered the crystallization of tin oxide and the products at a lower temperature of ⩽500°C found amorphous. The crystallinity of tin oxide increased with raising the calcination temperature to provide nanocrystalline cassiterite structure, whereas, increasing WO3 loading up to 25wt.% decreases the process. Careful control of calcination temperature and WO3 loading was found to have a critical effect on the specific surface area and therefore on the resulted surface acidity.The surface acidity measurements indicate that the catalysts possess very strong acid sites that designate both of Brønsted and Lewis acid sites.Catalytic application toward esterification of propionic acid with n-butanol was tested and the effect of various parameters, i.e., reaction temperature, reactant molar ratio, weight of the catalyst, WO3 loading and calcination temperature was also investigated. The highest conversion level was found for products loaded with 25wt.%WO3 and calcined at 400°C. Although both of Brønsted and Lewis acid sites are responsible for the reaction, the former acid sites found more effective on catalyzing the esterification reaction.

Calcium silicate/poly(ethylene terephthalate) biomaterials via ring-opening polymerization

Calcium silicate/poly(ethylene terephthalate) (CS/PET) composites were synthesized via ring-opening polymerization (ROP). CS raw material was synthesized by coprecipitation of calcium nitrate tetrahydrate and tetraethyl orthosilicate. Commercial grade PET was cyclodepolymerized under high dilution technique to cyclic oligo(ethylene terephthalate) (C-OET) raw material. The CS/PET pre-composites were prepared by mixing 60:40 (C6P4) and 50:50 (C5P5) wt% of CS powder and C-OET with the presence of 3 mol% of dibutyl tinoxide catalyst (with respect to the cyclic) then shaped the pre-composites into cylindrical pellets. The presented C-OET in the pre-composites was ring-opening polymerized to obtain PET film covering on the CS grains with the different reaction temperatures as 180, 200 and 250 °C under vacuum for 24 h. Thermogravimetric analysis indicated that the ROP-PET content in the C5P5 and C6P4 composites were about 46–48 and 35–38 wt%, respectively. The melting points (Tm) of ROP-PET of all composites were in a range of 233–246 °C. Compressive strength of the CS/PET composites was significantly increased from 4.8 MPa of the neat CS to 31.0 MPa for the C5P5 composites at the ROP temperature of 250 °C. The CS/PET composites faster induced the continuous-phase formation of hydroxyapatite (HAp) nanocrystals on their surfaces than the HAp/polymer composites. The induction occurred within 7-day soaked in the simulated body fluid (SBF) solution, indicating the bioactivity of the CS/PET composites.

Evaluation of Acidic Properties of Al<SUB>2</SUB>O<SUB>3</SUB> -Doped Sulfated Tin Oxide Catalyst in Esterification and Transesterification Reactions

Evaluation of Acidic Properties of Al<SUB>2</SUB>O<SUB>3</SUB> -Doped Sulfated Tin Oxide Catalyst in Esterification and Transesterification Reactions

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.

Strong metal–support interaction as activity requirement of palladium-supported tin oxide sol–gel catalyst for water denitration

Two nanocrystalline palladium-supported tin oxide catalysts for water denitration were synthesized by a modified sol–gel technique using appropriate chloride precursors for both support and active phases, and citric acid to tune the rate of hydrolysis and condensation. The difference among sample preparation procedures refers to the moment of the noble metal loading to the support, as well as to the calcination temperature altitude followed. Thus, mesoporous tin oxide was synthesized by a sol–gel method following calcination at 700°C. The palladium active phase was introduced afterwards by means of palladium chloride solution impregnation, followed by calcination at 400°C (sample 1). Alternatively, simultaneous complexation of both metal and support precursors followed by single calcination at 700°C was applied for preparation of sample 2. The former sample showed higher activity and selectivity in hydro-denitration of water model system initially containing 100 ppm of nitrates. This was explained by preferential textural, morphological and structural properties accomplished by early contact of metal and support nanoparticles, while achieved by calcination at high single temperature forcing diffusion of palladium ions into the tin oxide matrix. The outcome is very well distribution of palladium and strong metal–support interaction leading to multivalent tin. This indicates partly reduced tin oxide formation in the course of its reduction in hydrogen, which may act as active site in denitration reaction.