Sn Loading Research Articles

A novel BN supported bi-metal catalyst for selective hydrogenation of crotonaldehyde

A series of boron nitride (BN) supported Pt-Sn catalysts was prepared with a co-incipient wetness method employing hexachloroplatinic acid and tin(II) chloride. Pt loading was fixed at 1.1 wt%; Sn loading varied from 0.25 to 0.75 wt% on BN support. Selective hydrogenation of gas-phase crotonaldehyde was conducted in a steady-state flow reactor with temperatures ranging from 40 to 100 °C. The selectivity of crotyl alcohol reached over 80%. An optimum yield of crotyl alcohol reached 38% at 60% conversion of crotonaldehyde at 80 °C using Pt-Sn(0.75)/BN catalyst, while Pt-Sn(0.75)/γ-Al 2O 3 yielded less crotyl alcohol and a lower rate of crotonaldehyde conversion. The maximum yield rate of crotyl alcohol was 2.4 mmol/(g-cat. h) at 80 °C. Negligible deactivation was found during reaction for 4–6 h. The crystalline phases of PtSn and SnPt 3 alloys were observed from the XRD spectra of Pt-Sn/BN catalysts with various Sn loadings. The selectivity of crotyl alcohol increased with Sn loadings but the activity values of the catalysts went through a maximum. The H 2 reduction at 300 °C gave an optimum Pt–Sn alloy particle size so that the selectivity of crotyl alcohol increased without losing catalyst activity. The C O bond of crotonaldehyde was preferentially hydrogenated and the hydrogenation of C C bond was suppressed, resulting in the increase of crotyl alcohol selectivity.

Characterization and reactivity of stannum modified titanium silicalite TS-1 catalysts for transesterification of dimethyl oxalate with phenol

The transesterification of dimethyl oxalate (DMO) with phenol over stannum modified TS-1 was conducted to prepare methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO), which could be used to produce diphenyl carbonate (DPC). The component, structure and phase of TS-1 catalysts with various Sn loadings were investigated. The relationship between the catalytic properties and the Sn loadings was discussed. The results indicated that, although the Sn-modified TS-1 catalysts had fewer Lewis acid sites than the unmodified TS-1, its catalytic activity was increased greatly by the interaction of Sn with Ti–O–SiO 3 weak Lewis acid centers. The catalyst of TS-1 with 2 wt% Sn loadings performed best, giving 50.3% conversion of dimethyl oxalate and 99.2% selectivity to the target products. By means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX), the relationship between the catalytic properties and the structure of Sn dispersed on the surface of TS-1 was studied in detail. At Sn loadings below 2 wt%, Sn was highly dispersed, but at higher loadings it was crystallized into bulk tin dioxide, where the interaction between Ti and Sn was not evidently observed, leading to decreased catalytic activity. XPS results showed that Ti could not be detected even at 1 wt% Sn loadings. EDX results indicated that the content of Ti on the surface decreased with increasing Sn loadings, but the decrease in Ti content was much less than the increase in Sn content. Moreover, NH 3-TPD and FTIR analyses of adsorbed pyridine showed that there were only weak Lewis acid centers on all catalysts and the Sn loadings hardly affected the acid strength of the catalysts.

Differences in coke burning-off from Pt–Sn/Al 2O 3 catalyst with oxygen or ozone

Pt–Sn/γ-Al 2O 3 catalysts with different Sn loadings were prepared by incipient wetness coimpregnation of γ-Al 2O 3 with H 2PtCl 6 and SnCl 2. The Pt–Sn interaction was tested by temperature-programmed reduction and the catalytic activity was measured by cyclohexane dehydrogenation. The catalysts were coked by cyclopentane at 500 °C and totally or partially decoked with O 2 at 450 °C or O 3 at 125 °C. Coke deposits were studied by TPO and the catalytic activity of coked catalysts, partially or totally regenerated, by cyclohexane dehydrogenation. The TPO with O 3 shows that coke combustion with O 3 starts at a low temperature and has a maximum at 150 °C, that is a compensation between the increase of the burning rate and the rate of O 3 decomposition when increasing the temperature. Meanwhile O 2 burns coke with a maximum at 500 °C. When performing partial decoking with O 3 (125 °C) the remaining coke is more oxygenated and easier to burn than the coke that remains after decoking with O 2 (450 °C). After burning with O 3 the dehydrogenation activity of the fresh catalyst is recovered, while after burning with O 2 the activity is higher than that of the fresh catalyst. The burning with O 3 practically does not change the original Pt–Sn interaction while the burning with O 2 produces a decrease in the interaction, producing free Pt sites with higher dehydrogenation capacity. The differences in coke combustion with O 3 and O 2 are due to the different form of generation of activated oxygen, the species that oxidizes the coke. O 3 is activated by the γ-Al 2O 3 support at low temperatures firstly eliminating coke from the support while O 2 is activated by Pt at temperatures higher than 450 °C and the coke removal starts on the metal. Then, the recovery of the Pt catalytic activity as a function of coke elimination is faster with O 2 than with O 3.

Characterization and activity of stannum modified Hβ catalysts for transesterification of dimethyl oxalate with phenol

The transesterification of dimethyl oxalate (DMO) with phenol over stannum modified Hβ was conducted to prepare diphenyl oxalate (DPO) used to produce diphenyl carbonate (DPC). The component, structure and phase of Hβ catalysts with various Sn loadings were investigated. The relationship between the catalytic properties and the amount of Sn loadings was discussed. The catalyst of Hβ with 2 wt.% Sn loading based on metal performed best, giving 75.3% conversion of DMO and 24.0% selectivity to DPO. At Sn loadings below 2 wt.%, Sn was highly dispersed as monolayer, but at higher loadings it was crystallized into bulk tin dioxide, and the catalytic activity decreased. The curve of XPS peak intensity ratio of Sn 3d/Si 2p versus Sn loadings estimated the dispersed capacity of Sn on Hβ to be 2.1% Sn loading, which was in good agreement with the value obtained from XRD analysis. NH 3-TPD results showed that the amount of Sn loading had effect only on the strength of the weak surface acid sites on Hβ. And the decrease of selectivity to anisole was not due to the change of the weak acid sites. Maybe, SnO 2 accelerated to the formation of MPO and DPO. FTIR analysis of adsorbed pyridine showed that many Lewis acid sites and few Brönsted acid sites were present on Hβ catalysts with or without Sn modified. The acid sites together with SnO 2 active centers catalyzed the transesterification of DMO with phenol. Especially, SnO 2 active centers were in favor of the disproportionation of MPO into DPO.

Transesterification of Dimethyl Oxalate with Phenol under SnO2/SiO2 Catalysts

The transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was carried out over a SnO2/SiO2 catalyst. The evaluation results showed that SnO2/SiO2 had better activity and total selectivity to MPO and DPO than many conventional ester exchange catalysts. Especially, SnO2/SiO2 was in favor of the disproportionation of MPO into DPO compared with TS-1, MoO3/SiO2, and MoO3−SnO2/SiO2 catalysts. The conversion of DMO was 46.7% and the selectivity to DPO was 22.5% at 8% Sn loadings, which was the maximum at different Sn loadings. IR of adsorbed pyridine and NH3-TPD characterization indicated that the desirable catalytic activity of SnO2/SiO2 could be ascribed to its weak Lewis acidity. The structure and chemical state of tin species in SnO2/SiO2 had been investigated by X-ray diffraction. SnO2 active centers dispersed on a SiO2 carrier with a high specific surface area were of benefit to the transesterification.

Characterization and reactivity of silica-supported bimetallic molybdenum and stannic oxides for the transesterification of dimethyl oxalate with phenol

Abstract A series of bimetallic MoO3-SnO2/SiO2 catalysts with various Mo and Sn contents ranging from 1–16 wt.% were prepared by sequential impregnation with molybdate species and cationic Sn complexes using the wet impregnation method. The performance of these catalysts in the transesterification of dimethyl oxalate (DMO) with phenol was compared with corresponding stannum- and molybdenum-supported catalysts prepared by the same method. The results indicated that the catalyst of MoO3-SnO2/SiO2 with 14 wt.% Mo and Sn contents performed best, giving 74.6% conversion of DMO and 99.5% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The component, structure and phase of MoO3-SnO2/SiO2 catalysts with various Mo and Sn contents were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET specific surface area measurement, temperature-programmed desorption of ammonia (NH3-TPD), and FT-IR analysis of adsorbed pyridine. It was observed that interdispersion between MoO3 and SnO2 plays an important role in modifying the catalytic behavior. NH3-TPD and FT-IR analysis of adsorbed pyridine results showed that only weak Lewis acids were present on the catalyst surface and the amounts of Mo and Sn loadings has hardly effected the strength of the surface acid. The weak Lewis acid sites catalyzed transesterification of DMO with phenol and Sn gave a promotional effect.

Transesterification of dimethyl oxalate with phenol over TS-1 catalyst

The transesterification of dimethyl oxalate with phenol to produce methyphenyl oxalate and diphenyl oxalate was carried out in liquid phase using a heterogeneous catalyst. The evaluation results showed that TS-1 had better activity and excellent selectivity to target products compared with many conventional ester exchange catalysts tested. Two hours as the duration of the reaction was appropriate. Under the catalytic reaction conditions, framework IR and the reaction results jointly proved that the best calcination temperature was 823 K at which the amount of acid sites measured by IR of adsorbed pyridine reached a maximum. X-ray diffraction of TS-1 did not show much variation with changing calcination temperatures from 723 to 923 K. The characterization of the catalyst, by means of IR of adsorbed pyridine and NH 3-TPD indicated that the desired catalytic activity of TS-1 could be ascribed to its weak Lewis acidity. Tin modified TS-1 showed a better performance in activity and selectivity. The conversion of dimethyl oxalate was improved up to 50.3% when Sn loading was 2, while the selectivity was above 99% over all Tin modified TS-1 molecular sieves.

Study of Sn-Coated Graphite as Anode Material for Secondary Lithium-Ion Batteries

Tin-graphite composites have been developed as an alternate anode material for Li-ion batteries using an autocatalytic deposition technique. The specific discharge capacity, coulombic efficiency, rate capability behavior, and cycle life of Sn-C composites has been studied using a variety of electrochemical methods. The amount of tin loading and the heating temperature have a significant effect on the composite performance. The synthesis conditions and Sn loading on graphite have been optimized to obtain the maximum reversible capacity for the composite electrode. Heating the composite converts it from amorphous to crystalline form. Apart from higher capacity, Sn-graphite composites possesses higher coulombic efficiency, better rate capability, and longer cycle life than the bare synthetic graphite. Current studies are focused on reducing the first cycle irreversible capacity loss of this material. © 2002 The Electrochemical Society. All rights reserved.

Sol–Gel Prepared Sn–Al2O3 Catalysts for the Selective Reduction of NO with Propene

Abstract Catalytic reduction of NO by propene in the presence of oxygen was studied over Sn–Al2O3 prepared by the sol–gel method. The maximum NO conversion did not change much with Sn loading (1–5 wt%), although the effective temperature window for NO reduction shifted to lower temperatures with increasing Sn loading. X-ray diffraction (XRD), and X-ray absorption spectroscopy (XANES and EXAFS) revealed the formation of finely-divided SnO2 crystallites in Sn–Al2O3. It was deduced that not only the surface vicinity of supported SnO2, which can be reduced at lower temperatures, but also alumina participate in the reaction as catalytically active sites. The catalytic performance of Sn–Al2O3 was markedly improved by an H2O treatment at 873 K. The H2O treatment did not affect the crystal structure of the catalysts and the dispersion state of supported SnO2, but promoted the removal of Cl− ions, which originated from the SnCl4 precursor. The activity enhancement by the H2O treatment was accounted for by an increase in the surface SnO2 concentration as active sites and by the modification of oxo-tin species as active sites. Reaction kinetic studies suggested that NO reduction on the fresh and the H2O-treated catalysts proceeds through the same reaction pathway in which the surface NOx adspecies and C3H6-derived species play an important role for NO reduction.

XPS Study of the Adsorption of SO2 and NH3 over Supported Tin Dioxide Catalysts Used in de-NOx Catalytic Reaction

Alumina and titania supported tin dioxide catalysts presenting various Sn loadings were prepared by impregnation. The acidity and basicity of the samples were determined by adsorption of ammonia and sulfur dioxide, respectively, using adsorption microcalorimetry and X-ray photoelectron spectroscopy. The surface reactivity of the samples and the chemical composition of the adsorbed species were determined as well as the heats of adsorption of the probe molecules. The catalysts were tested in the selective catalytic reduction of NO by C2H4. Both calorimetry and XPS experiments have shown that the SnO2/TiO2 series of samples was markedly more acidic than the SnO2/Al2O3 series, as the N/(Ti+Sn) molar ratios were noticeably higher than the corresponding N(Al+Sn) ratios. The number of acidic sites seemed to increase with the tin content when tin dioxide was well dispersed on the support. They are of Lewis type. It was shown that sulfur dioxide adsorption led to the formation of three types of species: SO2, sulfites, and sulfates. The basicity of the SnO2/Al2O3 series of samples was weaker than that of the alumina support and passed through a minimum around 12 wt % Sn. On the contrary, as the acidity, the basicity of the SnTi series did not seem dependent on the Sn concentration. This can be correlated to the bad dispersion of SnO2 on TiO2. In the NO reduction by C2H4 reaction, the turnover frequency mainly depends on the Sn dispersion, and the Sn centers are very active even at low amounts.

Support Effects on de-NOx Catalytic Properties of Supported Tin Oxides

The influence of the carrier (i.e., SiO2, ZrO2, TiO2, γ-Al2O3, and MgO) on the reduction pattern, the acid–base properties, and the catalytic activity of supported tin dioxide catalysts has been investigated by temperature-programmed reduction/oxidation, adsorption calorimetry, and reduction of NOx by ethene in an oxygen-rich atmosphere. Two series of SnO2 catalysts of low (∼3 wt%) and high (∼20 wt%) Sn content were prepared by impregnation. The dramatic influence of the support on the activity and selectivity of the SnO2 surfaces in the NO reduction by C2H4 was evidenced. For the 3 wt% Sn series, 39, 38, 29, 24, and 0% conversions of 5000 ppm NO to N2 in the presence of 90,000 ppm of O2 at a space velocity of 50,000 h−1 were observed at 500°C on ZrO2, Al2O3, TiO2, SiO2, and MgO supports, respectively. The most active catalysts at low Sn loading were those based on ZrO2 and Al2O3. The integral N2 formation rates per mole of SnO2 ranged from 2 to 5×10−3 s−1 in the 350–500°C temperature domain. An increase of the Sn loading led to small positive or negative effects on the extent of the NO reduction depending on the support. A direct relationship between reducibility and catalytic activity has also been observed. Above monolayer coverage, the molecular structures of SnO2 play an important role. For the 20 Sn wt% series, the reducibility scale for SnIV→SnII, based on the temperature at the maximum of the reduction peak, is in the order SnSi-20>SnTi-20>SnAl-20>SnZr-20, while the competitiveness factor increases in the same order. Finally, it appears that a relatively strong acidity is necessary for good catalytic performance, but no direct correlation between the number of acid sites and the catalytic activity was observed.

Multitechnique study of the interaction of SO2 with alumina-supported SnO2 catalysts for lean NOx abatement

This study deals with the physicochemical characterization of SO 2 -treated alumina-supported tin dioxide surfaces as a function of the tin oxide loading. Three analysis techniques were used: Fourier transform infrared spectroscopy (FTIR), XPS and adsorption calorimetry. The two types of spectroscopies allowed the identification of the nature of the sulphur-containing species after SO 2 adsorption. The determination of the quantities of adsorbed sulphur-containing species was made possible by adsorption calorimetry and XPS. At 353 K the SO 2 uptake was minimum for 8 wt.% Sn and the major species were SO 3 2- . When increasing the Sn loading, the weakly adsorbed SO 2 species vanished whereas the amounts of sulphite species increased. Above 12 wt.% Sn, the presence of sulphate species increased, with a maximum for bulk SnO 2 . After desorption at 673 K, the SO 2 uptake was considerably decreased and each sample presented more SO 4 2- than SO 3 2- species.

Bimetallic Pt–Sn catalysts supported on activated carbon: I. The effects of support modification and impregnation strategy

A commercial activated carbon (AC) was used as a support either after washing with HCl or after further oxidation with air or HNO 3. The supports were characterized by N 2 adsorption, TPD and SEM. The results indicated the drastic change in physical and surface chemical properties of activated carbons due to the oxidation treatments. Three sets of catalysts were prepared on these supports. In each set, monometallic Pt/AC and bimetallic Pt–Sn/AC catalysts were prepared. Bimetallic catalysts were prepared either by coimpregnation or by sequential impregnation in which the Sn precursor was introduced first. In all catalysts, the Pt loading was kept fixed as 1 wt.%. Two levels of Sn loading, 0.25 and 0.50 wt.%, were applied in bimetallic samples. The catalysts were characterized by H 2 adsorption, TPR, SEM-EDX, XRD, XPS and tested in a structure insensitive reaction (benzene hydrogenation). The results indicated the pronounced changes in catalytic properties depending on the abundance of surface oxide groups of the supports and Pt–Sn interaction. Coimpregnation favored Pt–Sn interaction and alloy formation. The type of alloy formed was affected by the surface chemistry of the activated carbon; oxidized samples favored the formation of Pt 3Sn. XPS results indicated the migration of Pt from surface to interior sites which is driven by decomposition of oxygen bearing anchoring sites during the reduction. The migration was stabilized up to a point by the introduction of Sn as the second metallic phase and, as a consequence, by the Pt–Sn interaction. The interaction between metallic phases and alloy formation led to striking decreases in benzene hydrogenation activity, which indicates the lower amount of active Pt sites available. Very high H 2 adsorption capacities of bimetallic samples compared to their benzene hydrogenation activities point out to the H 2 adsorption capacities of the Pt–Sn alloys formed.

Characterization of SnO2/Al2O3 Lean NOx Catalysts

SnO2/Al2O3 prepared with SnCl2 impregnation onto sol–gel Al2O3 and calcined at 800°C is one of the most active catalysts for lean NOx reduction with propene under high partial pressures of O2 (15%) and H2O (10%) and space velocity (30,000 h−1). An unusual feature of this catalyst is the independence of maximum NO conversion over a wide range of Sn contents (1 to 10 wt% Sn). This catalyst is, however, sensitive to other preparation variables such as the nature of Sn precursor and the calcination temperature. X-ray photoelectron spectroscopic results indicate that Sn is present in the +4 oxidation state irrespective of Sn loadings. X-ray diffraction, temperature-programmed desorption, and temperature-programmed reduction results indicate a wide range of oxo–tin cluster sizes as well as different ratios of amorphous and crystalline SnO2 present in samples with different Sn loadings. The Sn(IV) in the amorphous SnO2 fraction can be reduced to Sn(II) below 450°C in the TPR experiments. In fact, all of the SnO2/Al2O3 catalysts have very similar H2 uptake features below 450°C. In view of the fact that they also have very similar catalytic properties, it appears likely that easily reducible amorphous SnO2 is an active phase for lean NOx catalysis in these samples.

Nanoscopic tin oxide films on mesoporous silica as novel catalysts for hydrogen transfer reactions

Deposition of tin-oxygen species on mesoporous silica (MCM-41) was achieved via chemical reaction of SnEt 4 vapour with surface silanol groups followed by heat treatment in air. At low Sn loading, EXAFS studies indicate six Sn-O interactions at an average distance of 2.043 Å and SnSi interactions at a distance of 3.791 Å. This suggests that SnO 6 octahedra were formed which anchored onto the surface of MCM-41 via Sn-O-Si bonds. At high Sn loading, tin oxide nanocrystallites (SnO 2) with rutile structure are evident (TEM, XRD). It was found that these mesoporous-silica supported tin oxides, after H 2 pre-treatment, showed higher activity than bulk SnO 2 supported on conventional silica in catalysing the hydrogen transfer reaction from a secondary alcohol to an unsaturated aldehyde.

Lean NOxCatalysis over Sn/γ-Al2O3Catalysts

Sn/γ-Al2O3were effective and highly stable catalysts for NO reduction with propene under high partial pressures of oxygen and water. The activity depended on the Sn loading. For a 10 wt% Sn/Al2O3at 475–500°C, 58% conversion of 1000 ppm NO to N2was obtained in the presence of 10% water and 15% O2, at a space velocity of 30,000 h−1, and 77% conversion at 15,000 h−1. The NO conversion increased with O2partial pressure but was suppressed by water below 500°C. The activity was also suppressed by SO2but could be restored slowly after the removal of SO2.

Structural and electronic properties of Sn overlayers and [formula omitted] surface alloys on Pd(111)

The first two layers of Sn deposited on Pd(111) at 300 K grow in layer-by-layer fashion after which crystallite formation commences. The electronic properties of these overlayers are dependent on the size of the 3D Sn islands. The occurrence of Sn→Pd valence charge-transfer is inferred, due allowance being made for initial and final state effects in the photoemission data. Evidence is presented for a significant Pd surface core-level shift enhancement by Sn of ≈0.7 eV. Depending on the initial Sn loading, heating generates stable monolayer (Pd 2Sn) or multilayer (Pd 3Sn) surface alloys exhibiting √3 and (2 × 2) periodicities, respectively. The very different CO adsorption capacity of these two phases indicates that on Pd Sn alloy surfaces, only pure Pd threefold hollow-sites are capable of strongly chemisorbing CO.

Nano-characterization of Rh-Sn bimetallic catalysts

Bimetallic catalysts are of considerable importance because they possess both high activity and selectivity. Recently, there has been considerable interest in bimetallic catalysts produced by surface organometallic chemistry on metals. A detailed description of the structure and composition at the nanometer level is critical to fully understand the behavior of such catalysts. We have undertaken a study of the microstructure of Rh-Sn/SiO2 bimetallic hydrogenation catalysts.A Rh-Sn precursor was prepared by reacting tetrabutyltin with a silica supported Rh parent catalyst (1 %Rh/SiO2). The bimetallic catalysts were produced by thermal decomposition of the precursor in flowing hydrogen at 623 K. Five different catalysts were produced with a range of different Sn loadings from Rh(1%)/SiO2 to Rh(1%)-Sn(1.85%)/SiO2. The resulting bimetallic catalysts were able to selectively hydrogenate isolated and conjugated C=O functional groups. In situ XPS showed that the Sn and Rh were in the fully reduced state. Mossbauer spectroscopy studies confirmed that Sn was present in the zerovalent state indicating that no oxidized Sn was present. Preliminary IR data suggests that most of the Rh atoms are isolated from their neighbors (presumably by Sn).