SnOx Species Research Articles

Evolution of the Active Phase of Pt/Sn-Al2O3 Catalysts During Acidic Impregnation and Their Use in Propane Dehydrogenation.

Alumina-supported PtSn is an industrialized catalyst for propane dehydrogenation. During the catalyst impregnation, the acidic impregnation solution with chloroplatinic acid as a precursor inevitably leads to the partial dissolution of the surface of amphoteric alumina support and finally varies catalytic performance. Herein, the structure evolution of the active phase, induced by an impregnated acidic solution, was studied with special care. According to the diffused double layer theory, we proposed a model of microgels during impregnation. The microgels formed in the solution with suitable acidity on the surface of the catalysts evolved into a structure of Al2O3-coated oxidized Pt by reprecipitation during drying and calcination. The covered Pt species could be exposed by Ar+ sputtering or migrate to the surface during reduction to serve as active sites for propane dehydrogenation. Noticeably, the surface Sn0 species was generated when the pH of the impregnated solution was around 0.56, which is solid proof for the unique active phase with the PtSn alloy present on SnOx species existing on the surface of the Sn-Al2O3 support. The synthesized catalyst exhibited high propylene selectivity (99.4%) and superior stability (kd = 0.002 h-1). This study provides new insight for the precise preparation of Pt/Sn-Al2O3 catalysts.

Molten salt induced synthesis of Ni-Sn-Al ternary oxide as highly efficient catalyst for low S/C ratio methane steam reforming

Until now almost 50% of the world's hydrogen production at industrial level is realized by methane steam reforming (SMR). Traditionally a high steam to carbon ratio (S/C = 2.5–3.0) is needed to reduce coke formation on catalyst surface while adversely derives downsides like high energy input and significant gas dilution. Such dilemma in SMR process could be relieved by using low S/C ratio (<1.0) but instead raises the bar for catalyst anti-coking ability. In this work, we employed a facile method of molten salt with ball milling pretreatment to prepare Ni-Sn-Al ternary oxide. The synthesized sample showed high reaction activity with slight carbon deposition, benefiting from the well-dispersed Ni nanoparticles and the addition of Sn promoter. The molten salt was found to provide liquid environment and thus induce space confinement for Ni dispersion via strong NiO bond. The positive role of SnOx species is evidenced by comparing the catalytic stability of NiAl binary oxide and Ni-Sn-Al ternary oxide, which the latter is with strong coke resistance under the 30-h stability test without obvious deactivation. Time-resolved in-situ DRIFTS reveals different reaction routes over the two catalysts. Our approach offers a new strategy of dissolving the severe coke formation issue during low S/C ratio SMR.

Niobium- and Tantalum-Doped Pt-Sn/Al2 O3 as Efficient Catalysts for Propane Dehydrogenation.

The Pt-Sn/Al2 O3 catalyst has been successfully commercialized for propane dehydrogenation, but it is still highly desirable to further improve its catalytic performance for maximizing the utilization efficiency of noble metal Pt. Herein, this work demonstrates that doping Nb and Ta into Pt-Sn/Al2 O3 has great impacts on its structure, and significantly improved catalytic performances are achieved in Pt-Sn-X/Al2 O3 (X=Nb and Ta). It is found that the incorporation of Nb and Ta into Pt-Sn/Al2 O3 can promote the dispersion of Pt-Sn particles, which results in Pt-Sn clusters being highly dispersed at the surface of Al2 O3 . Moreover, the presence of Nb and Ta makes the SnOx species less reducible, and thus the Pt-Sn particles become more stable at high temperature. Systematic exploration allows to obtain the optimized Pt-Sn-Nb5.0 /Al2 O3 and Pt-Sn-Ta1.0 /Al2 O3 , and these two catalysts exhibit high initial propane conversion (above 43.8 % and 50.4 %) with propylene selectivity of above 98 %. Most importantly, they show excellent regeneration in propane dehydrogenation, and their catalytic performance can be completely restored by a simple calcination.

Selective production of acetol or methyl lactate from cellulose over RuSn catalysts

Designing a catalytic system that could convert cellulose to switchable C3 alcohols or esters with controllable selectivity is highly desired to meet the rapidly changing market demand. Herein, we develop RuSn catalysts with the altering Sn loadings that can achieve acetol formation from cellulose hydrogenation at 240 °C in presence of H2 or yield methyl lactate production from cellulose conversion in methanol and water mixture at 200 °C in presence of N2. The increased Sn contents from 3% to 6% lead to form different surface sites from Ru3Sn7, Ru, and SnOx to Ru3Sn7 and SnOx. The integrated Ru3Sn7, Ru, and SnOx species on 1.5%Ru-3%Sn/SiO2 catalyze isomerization, retro-aldol condensation, and hydrogenation individual steps with coordinated reaction rates, resulting in the acetol formation with a high yield of 53.7C%. Furthermore, the optimum combination of Ru3Sn7 and SnOx on 1.5%Ru-6%Sn/SiO2 contributes to the isomerization, retro-aldol condensation, dehydration, and 1,2-hydride shift, giving rise to the preferential production of methyl lactate at a 25.1C% yield. These results illustrate the feasibility of controlling the selective conversion of cellulose to C3 acetol or methyl lactate by devising a tunable catalytic system, which guides the rational design of catalysts for the selective conversion of cellulose.

Platinum-Tin/Tin Oxide/CNT Catalysts for High-Performance Electrocatalytic Ethanol Oxidation.

Ethanol is a promising liquid clean energy source in the energy conversion field. However, the self-poisoning caused by the strongly adsorbed reaction intermediates (typically, CO) is a critical problem in ethanol oxidation reaction. To address this issue, we proposed a joint use of two strategies, alloying of Pt with other metals and building Pt/metal-oxide interfaces, to achieve high-performance electrocatalytic ethanol oxidation. For this, a well-designed synthetic route combining wet impregnation with a two-step thermal treatment process was established to construct PtSn/SnOx interfaces on carbon nanotubes. Using this route, the alloying of Pt-Sn and formation of PtSn-SnOx interfaces can simultaneously be achieved, and the coverage of SnOx thin films on PtSn alloy nanoparticles can be facilely tuned by the strong interaction between Pt and SnOx . The results revealed that the partial coverage of SnOx species not only retained the active sites, but also enhanced the CO anti-poisoning ability of the catalyst. Consequently, the H-PtSn/SnOx /CNT-2 catalyst with an optimized PtSn-SnOx interface showed significantly improved performances toward the ethanol oxidation reaction (825 mA mgPt -1 ). This study provides deep insights into the structure-performance relationship of PtSn/metal oxide composite catalysts, which would be helpful for the future design and fabrication of high-performance Pt-based ethanol oxidation reaction catalysts.

Tuning the Product Selectivity of the Cu Hollow Fiber Gas Diffusion Electrode for Efficient CO2 Reduction to Formate by Controlled Surface Sn Electrodeposition.

The efficient CO2 electrochemical reduction reaction (CO2RR) relies not only on the development of selective/active catalysts but also on the advanced electrode configuration to solve the critical issue of poor CO2 mass transport and derived sluggish cathodic reaction kinetics. In this work, to achieve a favorable reaction rate and product selectivity, we designed and synthesized an asymmetric porous Cu hollow fiber gas diffusion electrode (HFGDE) with controlled Sn surface electrodeposition. The HFGDE derived from the optimal Sn electrodeposition condition exhibited a formate Faradaic efficiency (FE) of 78% and a current density of 88 mA cm-2 at -1.2 V versus reversible hydrogen electrode, which are more than 2 times higher than those from the pristine Cu HFGDE. The achieved performance outperformed most of the other Sn-based GDEs, indicating the creation of sufficient contact among CO2, electrolyte, and electrode catalyst through the design of the hollow fiber pore structure and catalytic active sites. The enhancement of formate production selectivity and the suppression of the hydrogen by-product were attributed to the optimized ratio of SnOx species on the electrode surface. The best performance was seen in the HFGDE with the highest Sn2+/Sn4+ (120 s deposition), likely due to the modulating effect of the Cu substrate via electron donation with Sn species. The selectivity control strategy developed in the asymmetric HFGDE provides an efficient and facile method to stimulate selective electrochemical reactions in which the gas-phase reactant with low solubility is involved.

Effect of Aging Temperature of Support on Catalytic Performance of PtSnK/Al2O3 Propane Dehydrogenation Catalyst

Catalytic dehydrogenation of propane to propylene is one of the vital processes in the petrochemical industry, primarily because of the extensive use of propylene as one of the most crucial building blocks for the production of a wide range of essential chemicals and polymers. In this study, the nano-structural PtSnK was supported on an alumina carrier prepared by an environmentally friendly modified oil-drop method. By adjusting the aging temperature of the alumina carrier, the physical and chemical structural properties of the catalyst can be modulated, and then affect the propane dehydrogenation performance of the catalyst. The effects of aging temperature on the structure and chemical properties of the support and catalyst were studied by N2 sorption, XRD, TEM, TG, NH3-TPD, H2-TPR, CO pulse adsorption, and XPS techniques. As the aging temperature increases, the spherical particles gradually changed from a worm-like structure to a needle or rod-like structure. At the same time, the pore size and volume increase, the pore size distribution becomes wider. Besides, the aging temperature also affects the interaction between the supported metal and the alumina support. The higher aging temperature can inhibit the reduction of SnOx species and enhance the interaction between Sn species and the alumina support. All these features together ensure excellent propane dehydrogenation performance and high stability of the catalyst. When the aging temperature is 140 °C, the PtSnK/Al2O3 catalyst exhibits excellent catalytic propane dehydrogenation performance, with an average propane conversion of 36.5%, average propylene selectivity of 96.5% during 50 h reaction. We reported the modulation of the aging temperature on the physical and chemical properties of the PtSnK/Al2O3 propane dehydrogenation catalyst when the alumina carrier is prepared by the oil-drop method. In order to obtain an optimal propane dehydrogenation catalyst, an optimum aging temperature is preferred to provide a catalyst with high propane conversion, propylene selectivity and catalyst stability.

K-modified Sn-containing dendritic mesoporous silica nanoparticles with tunable size and SnOx-silica interaction for the dehydrogenation of propane to propylene

Sn-containing dendritic mesoporous silica nanoparticles (Sn-DMSNs) were successfully prepared by the in-situ co-assembly method. Sn-DMSNs preserve original structural characteristics with three-dimensional and center-radial pore structure. The nanoparticle sizes of Sn-DMSNs can be controlled systematically from 170 nm to 360 nm depending on the molar ratio of NaSal/CTAB. Sn species are incorporated into the matrix of silica and the highly dispersed SnOx species are achieved. Sn-DMSNs catalysts exhibit excellent catalytic performance and stability in the propane dehydrogenation. The highly dispersed SnOx species rather than polymeric SnOx or crystalline SnO2 species contribute to the activation of propane and formation of propylene. The molar ratio of NaSal/CTAB also shows an important role in the structure of support and SnOx species. The excellent stability of Sn-DMSNs catalysts can be ascribed to the good ability to restrain coke formation and strong interaction between SnOx species and silica. The effect of potassium on Sn-DMSNs catalyst is also investigated.

Surface reconstruction of Pt–Sn nanoparticles supported on Al2O3 in the presence of carbon monoxide

FTIR spectroscopy and volumetric measurements are used to study the adsorption of CO (mainly 1% CO/He) in the temperature range 300–713 K on a 1.2% Pt–2.7% Sn/Al2O3 solid reduced in H2 at 713 K leading from XRD to PtSn bimetallic particles. This reveals the changes in the adsorption properties of the Pt sites for CO adsorption by comparison with monometallic Pt/Al2O3 solids and the stability of the Pt–Sn bimetallic particles in the presence of CO. At 300 K, FTIR spectroscopy shows that the insertion of Sn leads to (a) the total disappearance of the Pt sites forming bridged CO species (ascribed to a geometric effect of Sn) and (b) a significant shift in the position of the IR band of linear CO species on Pt sites from 2066 to 2044 cm−1 on Pt and Pt–Sn particles, respectively, ascribed to different adsorbed species, namely LPt and L1Pt–Sn, respectively. Moreover, it is shown that the insertion of Sn is associated with the decrease in the amount (in µmol/g of platinum) of Pt adsorption sites for CO adsorption. The evolution of the IR band of the L1Pt–Sn CO species with the increase in Ta in isobaric conditions reveals a modification of the surface of the Pt–Sn particles for Ta > ≈ 460 K ascribed to enrichment in Pt° due to a surface reconstruction. The Pt sites of the reconstructed surface are characterized by an IR band at 2057 cm−1 after adsorption of CO at 300 K ascribed to a linear CO species named L2Pt–Sn. The reconstructed surface is stable in the presence of CO in the range 300–713 K and disappears by hydrogen reduction at 713 K. Successive surface reconstruction/hydrogen reduction at 713 K cycles lead to an ageing of the Pt–Sn particles associated with a progressive decrease in the amount of Pt° sites on the freshly prepared and reconstructed Pt–Sn particles. It is shown that the reconstruction of the Pt–Sn particles is probably due to the formation of SnOx species via oxygen species coming mainly from the hydroxyls groups of the support.

Aromatization of n-Butane and i-Butane over PtSnK/ZSM-5 Catalysts: Influence of SiO2/Al2O3 Ratio

This work reports on the effect of SiO2/Al2O3 ratio (25, 38, 50 and 80) on the physicochemical properties and performance of PtSnK/ZSM-5 catalysts in butanes aromatization process. It was found that the Pt dispersion decreased obviously with SiO2/Al2O3 increasing. The strength and type of acid sites look similar, while the redox properties were influenced significantly. The Pt–SnOx species are produced except for PtSnK/ZSM-5-80 with large separated Pt ensembles from H2-TPD analysis. The PtSnK/ZSM-5-50 catalyst shows the improved cofeeding (mixed butanes: 50 wt% n-butane + 50 wt% i-butane) conversion (88%) with lower Pt dispersion (25%). Furthermore, dehydrogenation of mixed butanes over Pt–SnOx is more favorable on PtSnK/ZSM-5-50 when both ratios of benzene/C8 aromatics and methane/propane are high, due to the outside contact time is short. So the influence of SiO2/Al2O3 ratio on the aromatics distribution is mainly related to the difference in the Pt dispersion and distribution. However, the predominate process to produce light aromatics (BTX) is still hydrogen transfer, which contributes to the long-life span.

CO dissociation on Pt-Sn nanoparticles triggers Sn oxidation and alloy segregation

Identifying the causes of the segregation of Pt-based alloy nanoparticles is crucial for the design and operation of the corresponding catalysts and electrodes. This article describes a yet unreported mode of alloy segregation upon exposure to CO. In situ IR studies indicated that Pt-Sn alloy nanoparticles were not stable under (i) H2-free CO at any temperature or (ii) CO/H2 mixtures at temperatures below ca. 450 K. This was rationalized by the ability of Pt to dissociate CO. The oxygen adatoms readily reacted with metallic Sn to form a SnOx species, leading to Pt-Sn segregation, alongside carbon deposition. XPS and XANES analyses confirmed Sn reoxidation. While a contamination by traces of O2 at the sub-ppm level cannot be excluded, the data reported indicate that the structural modifications undergone by the Pt-Sn nanoparticles are more consistent with a reaction involving CO rather than one involving O2. In particular, the XPS analysis after CO exposure revealed an increased fraction of graphitic carbon, while that of oxidized carbon decreased. Thermodynamic calculations indicate that the oxidation of tin by CO, with concomitant carbon formation (Sn + CO → SnO + C) is as favourable as Boudouard reaction (2 CO → CO2 + C) at low temperatures. Alloy stability in the presence of CO must therefore be a concern when CO dissociation is possible and one of the alloyed metal is oxophilic.

Sn and Zn modified HZSM-5 for one-step catalytic upgrading of glycerol to value-added aromatics: Synergistic combination of impregnated Sn particles, ALD introduced ZnO film and HZSM-5 zeolite

The chemoselective catalytic conversion of glycerol into high value-added aromatics (GTA) can greatly enhance the economic profits in biodiesel and biomass industry chain. In order to enhance the aromatization activity, stability and conversion efficiency of carbon in glycerol into aromatics during the GTA process, Zn species, which could directly convert alkenes originated from deoxygenation of glycerol into aromatics through dehydrogenation reaction, was introduced into Sn/HZSM-5 zeolite via atomic layer deposition (ALD) and incipient wet impregnation (IWI) method. Compared with impregnated ZnO modified Sn/HZSM-5, ZnO introduced by 20 ALD cycles into Sn/HZSM-5 deposited in the form of thin film, which not only fully coated both HZSM-5 external and internal surface, but also partially covered impregnated Sn particles. This film stabilized the oxidation state of loaded SnOx species which acted as catalytically active materials and further healed HZSM-5 structural defects, leading to the better synergistic effect among HZSM-5 zeolite, impregnated Sn particles and ALD introduced ZnO films. Besides, the reusability of this catalyst could be tremendously improved due to the protective effect of introduced ALD ZnO film which could prevent irreversible dealumination of HZSM-5 from exposure of HZSM-5 framework to steam during GTA reaction and regeneration procedure. However, when the deposited ZnO ALD cycle number reached 40, Sn particles on HZSM-5 could be completely packaged by ZnO film, on which occasion Sn could not participate in the GTA process, thereby leading to the reduction in both aromatics yields and catalyst lifetime.

Electrocatalysis of Direct Methanol and Ethanol Oxidation in Polymer Electrolyte Fuel Cells

In recent decades, significant efforts have been focused on the direct electrochemical oxidation of alcohol and hydrocarbon fuels. Organic liquid fuels are characterized by high energy density and the electromotive force associated with their electrochemical combustion to CO2 is comparable to that of hydrogen combustion to water. Among the liquid organic fuels, methanol and ethanol have promising characteristics in terms of reactivity at low temperatures, storage and handling. Compared with ethanol, methanol has the significant advantage of faster reaction kinetics and higher selectivity to CO2 formation for the electrochemical oxidation process. Highly dispersed carbon-supported bimetallic PtRu and PtSn alloy catalysts are widely recognized among the most performing anode formulations for these processes. Alloying Pt with Ru and Sn promotes oxidation of methanol and ethanol by the adsorption of OH species at considerably lower overpotentials and, thus, favoring the occurrence of a bifunctional mechanism. Furthermore, the electronic effect caused by a second metal on the neighboring Pt atoms affects the strength of CO adsorption on the catalyst surface. This causes a decrease of the coverage of poisoning CO intermediate species. Catalysts characterized by a high degree of alloying and metallic behavior on the surface appear to be very active towards methanol oxidation. However, beside the alloyed catalysts, noble metal oxides (IrOx, RuOx) and valve metal oxides (SnOx, TiOx and VOx) can be suitable promoters for methanol and ethanol oxidation in acidic environment. An effective use of such oxide promoters in combination with the alloy catalysts can provide a multifunctional catalytic system. Recent studies carried out in our laboratory have shown that IrOx can give rise to a significant promoting effect, even larger than that of RuOx, both in the case of methanol and ethanol oxidation. Whereas, the electrocatalytic enhancement produced by the valve metal oxides is generally lower than IrOx and RuOx but well evident. These results are interpreted in terms of the different water displacement mechanisms for the various oxides and the related effects on adsorbed CO removal. The effect of temperature is also discussed with reference to the coverage of adsorbed methanolic residues or change in selectivity in the case of ethanol electro-oxidation. For the ethanol oxidation process, anode catalyst selectivity towards CO2, acetic acid and acetaldehyde reaction products is discussed in relation to the alloy and oxide content in the catalyst. In particular, SnOx species on the surface of Sn-rich Pt-Sn-based electrocatalyst appear to assist the further oxidation of ethanolic adsorbates, leading to larger yields of acetic acid and CO2. In addition to the enhancement of reaction rates, there is an effect of the promoter on the stability of the bimetallic alloy as evidenced by accelerated stress tests. All these evidences seem to indicate that a multifunctional catalyst may represent a valid route to enhance performance and reliability of methanol and ethanol electro-oxidation processes at low temperature.

Selective Hydrogenation of m-Dinitrobenzene to m-Nitroaniline over Ru-SnOx/Al2O3 Catalyst

Series catalysts of Ru-SnOx/Al2O3 with varying SnOx loading of 0–3 wt% were prepared, and their catalytic activity and selectivity have been discussed and compared for the selective hydrogenation of m-dinitrobenzene (m-DNB) to m-nitroaniline (m-NAN). The Ru-SnOx/Al2O3 catalysts were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and hydrogen temperature-programmed reduction (H2-TPR) and desorption (H2-TPD). Under the modification of SnOx, the reaction activity increased obviously, and the best selectivity to m-NAN reached above 97% at the complete conversion of m-DNB. With the increasing of the SnOx loading, the amount of active hydrogen adsorption on the surface of the catalyst increased according to the H2-TPD analysis, and the electron transferred from Ru to SnOx species, as determined by XPS, inducing an electron-deficient Ru, which is a benefit for the absorption of the nitro group. Therefore, the reaction rate and product selectivity were greatly enhanced. Moreover, the Ru-SnOx/Al2O3 catalyst presented high stability: it could be recycled four times without any loss in activity and selectivity.

Synthesis of magnesium-modified mesoporous Al2O3 with enhanced catalytic performance for propane dehydrogenation

Magnesium (Mg)-modified mesoporous alumina with different type and content of Mg was prepared and then used as the support for platinum-tin catalyst in propane dehydrogenation. It was found that the property of Mg in Al2O3 varied with the way of the addition of Mg precursors. For the grafted Mg species, the connection between Al2O3 and Mg was increased by the forming of Mg–O–Al bonds in the inner surface of Al2O3 pore. While for the traditional impregnation, Mg was attached loosely to the outer Al2O3 surface by the aggregation of MgO. Moreover, modifying the internal framework of Al2O3 by suitable content of Mg can enhance the interaction between Sn and support, leading to more amounts of tin in their oxidized states, which was beneficial to enhance the interaction of Pt with SnOx species. As a result, agglomerations of metallic particles were suppressed and the catalyst exhibited the best catalytic performance in terms of activity and stability.

Ternary Pt/SnOx/TiO2 photocatalysts for hydrogen production: consequence of Pt sites for synergy of dual co-catalysts

A variety of ternary nanoheterostructures composed of Pt nanoparticles (NPs), SnOx species, and anatase TiO2 are designed elaborately to explore the effect of interfacial electron transfer on photocatalytic H2 evolution from a biofuel-water solution. Among numerous factors controlling the H2 evolution, the significance of Pt sites for the H2 evolution is highlighted by tuning the loading procedure of Pt NPs and SnOx species over TiO2. A synergistic enhancement of H2 evolution can be achieved over the Pt/SnOx/TiO2 heterostructures formed by anchoring Pt NPs at atomically-isolated Sn-oxo sites, whereas the Pt/TiO2/SnOx counterparts prepared by grafting single-site Sn-oxo species on Pt/TiO2 show a marked decrease in the rate of H2 evolution. The characterization results clearly reveal that the synergy of Pt NPs and SnOx species originates from the vectorial electron transfer of TiO2 → SnOx → Pt occurring on the former, while the latter results from the competitive electron transfer from TiO2 to SnOx and to Pt NPs.

Single-site Sn-grafted Ru/TiO2 photocatalysts for biomass reforming: Synergistic effect of dual co-catalysts and molecular mechanism

This work offers an engineering guide to obtaining highly efficient photocatalysts for hydrogen production. Synergetic enhancement of photocatalytic hydrogen evolution from biomass/water solution is achieved by co-modifying anatase TiO2 with single-site Sn-oxo species and RuO2 nanoparticles. Detailed characterization and analysis clearly reveal that such TiO2-based composites can function as photoelectrolysis cells, where RuO2 and SnOx species serve, respectively, as an anode and a cathode and TiO2 is mainly responsible for the conversion of photons into electrical energy and the OH formation. Electron paramagnetic resonance and infrared spectroscopy studies suggest a free radical reaction pathway triggered by the hole oxidation for the photocatalytic reforming of biomass. The CxHyOz renewables undergo one or more processes for the sequential oxidation of alcohol to aldehyde, acid, and finally CO2 and CO. The activity results indicate that proton reduction is the controlling-rate step of the overall photoreforming reaction.

Propane dehydrogenation over PtSnNa/La-doped Al2O3 catalyst: Effect of La content

La-doped mesoporous alumina (La-Al) with different content of La was synthesized and then this kind of material was used as the support for platinum–tin catalyst in propane dehydrogenation. It was found that a portion of La had been incorporated into the alumina framework with La-doping. When the content of La in the support was suitable, both the catalyst acidity and the coke amount were decreased. Moreover, in these cases, the presence of La could not only promote the distribution of metallic particles, but also strengthen the interaction between tin species and support. As a result, more amounts of tin could exist in oxidized states, which was beneficial to enhance the interaction of Pt with SnOx species and the reaction activity. In the current study, the PtSnNa/La-Al catalyst with 1.0wt.% La exhibited the best catalytic activity and stability. Compared with pure Al2O3 support, this La-doped Al2O3 support was also favorable for the improvement of the catalytic performance even at higher reaction temperature (605°C). However, with the excessive addition of La, the agglomerations of metallic particles and the increase in percentage of metallic tin (Sn0) on the catalyst were found, which seriously resulted in the deactivation of catalyst.

Promoting effect of SnOxon selective conversion of cellulose to polyols over bimetallic Pt–SnOx/Al2O3catalysts

Cellulose is the most abundant source of biomass in nature, and its selective conversion into polyols provides a viable route towards the sustainable synthesis of fuels and chemicals. Here, we report the marked change in the distribution of polyols in the cellulose reaction with the Sn/Pt atomic ratios in a wide range of 0.1–3.8 on the SnOx-modified Pt/Al2O3 catalysts. Such a change was found to be closely related to the effects of the Sn/Pt ratios on the activity for the hydrogenation of glucose and other C6 sugar intermediates involved in the cellulose reaction as well as to the notable activity of the segregated SnOx species for the selective degradation of the sugar intermediates on the Pt–SnOx/Al2O3 catalysts. At lower Sn/Pt ratios of 0.1–1.0, there existed electron transfer from the SnOx species to the Pt sites and strong interaction between the catalysts, as characterized by temperature-programmed reduction in H2 and infrared spectroscopy for CO adsorption, which led to their superior hydrogenation activity (per exposed Pt atom), and in-parallel higher selectivity to hexitols (e.g. sorbitol) in the cellulose reaction, as compared to Pt/Al2O3. The hexitol selectivity reached the greatest value of 82.7% at the Sn/Pt ratio of 0.5, nearly two times that of Pt/Al2O3 at similar cellulose conversions (∼20%). As the Sn/Pt ratios exceeded 1.5, the Pt–SnOx/Al2O3 catalysts exhibited inferior hydrogenation activity (per exposed Pt atom), due to the formation of the crystalline Pt–Sn alloy, which led to the preferential conversion of cellulose to C2 and especially C3 products (e.g. acetol) over hexitols, most likely involving the isomerization of glucose to fructose and retro-aldol condensation of these sugars on the segregated SnOx species, apparently in the form of Sn(OH)2. These findings clearly demonstrate the feasibility for rational control of the cellulose conversion into the target polyols (e.g. acetol or propylene glycol), for example, by the design of efficient catalysts based on the catalytic functions of the SnOx species with tunable hydrogenation activity.

Synthesis of Pt and Pt–Sn catalysts supported on H-Y zeolite induced by microwave radiation

The purpose of this study was the preparation of Pt and Pt–Sn catalysts supported on a HY zeolite (Si/Al=3) induced by microwave radiation as heating source. The solids were characterized by means of X-ray diffraction (XRD), elemental chemical analysis, nitrogen physisorption at −196°C, and X-ray photoelectron spectroscopy (XPS). Catalytic activity of the solids was evaluated using the toluene hydrogenation reaction. The XRD analysis showed that the zeolite structure was maintained after metal deposition. XPS revealed the presence of Pt0 species in monometallic catalyst, while in bimetallic Pt–Sn catalysts, Pt0 and SnOx species were found, which seem to be strongly interacting. The toluene hydrogenation reaction showed a drastic decrease in activity for bimetallic Pt–Sn catalyst, which was attributed to either a geometric and/or electronic interaction taking place on the Pt sites and tin species, avoiding, toluene adsorption.