Supported PtSn Catalysts Research Articles

Spatial segregation of three-dimensional Al2O3 supported PtSn catalyst for improved sintering-resistant at high temperature

Many catalytic reactions operate within high-temperature environment, inevitably leading to the sintering of small nanoparticles. Consequently, the design of sintering-resistant metal nanocatalysts at elevated temperatures pose significant challenges. Herein, we introduce an approach, employing a 3D flower-shaped Al2O3 (F-Al2O3), to stabilize nanoparticles by establishing a spatial separation in propane dehydrogenation (PDH). The PDH reaction conducted is just a test system at non-relevant conditions. Both ex-situ and in-situ TEM analyses evidence that PtSn nanoparticles on the F-Al2O3 exhibit remarkable resistance to sintering under high-temperature oxidative and reductive conditions. The propane conversion of PtSn/F- Al2O3 fully rebounds to its initial state and the average particle diameter of PtSn/F- Al2O3 remains virtually unchanged after seven PDH cycles. In contrast, 2D Al2O3 nanosheets (C-Al2O3) experience severe PtSn nanoparticle sintering. Computational studies highlight the effectiveness of the 3D flower-shaped Al2O3 in obstructing particle migration and ripen through spatial segregation. This strategy involving the construction of three-dimensional space support presents a promising avenue for the design of sintering-resistant nanocatalysts.

Dendritic Mesoporous Silica Nanoparticle Supported PtSn Catalysts for Propane Dehydrogenation.

PtSn catalysts were synthesized by incipient-wetness impregnation using a dendritic mesoporous silica nanoparticle support. The catalysts were characterized by XRD, N2 adsorption-desorption, TEM, XPS and Raman, and their catalytic performance for propane dehydrogenation was tested. The influences of Pt/Sn ratios were investigated. Changing the Pt/Sn ratios influences the interaction between Pt and Sn. The catalyst with a Pt/Sn ratio of 1:2 possesses the highest interaction between Pt and Sn. The best catalytic performance was obtained for the Pt1Sn2/DMSN catalyst with an initial propane conversion of 34.9%. The good catalytic performance of this catalyst is ascribed to the small nanoparticle size of PtSn and the favorable chemical state and dispersion degree of Pt and Sn species.

Efficient supported Pt-Sn catalyst on carambola-like alumina for direct dehydrogenation of propane to propene

A carambola-like Al2O3 (Al2O3-mel) has been prepared via a facile complex assisted hydrothermal approach by using melamine-Al(NO3)3 complex as Al precursor, template, and precipitant, which generates an excellent carrier for preparing the supported Pt-Sn catalyst (Pt-Sn/Al2O3-mel) with outstanding catalytic performance in propene production through direct dehydrogenation of propane. Pt-Sn/Al2O3-mel shows 2.1 and 1.8 times higher turnover frequency (TOF, 22.5 s−1) with 99.1% of high selectivity and high stability towards propene synthesis than the supported Pt-Sn catalysts on the Al2O3-amm prepared by using the traditional hydrothermal process with Al(NO3)3 as Al precursor and ammonium hydroxide as precipitant and the commercially available Al2O3-com as support for Pt-Sn catalyst, respectively. Various characterization techniques were employed to probe the relationship of structure-performance of supported Pt-Sn catalyst on different Al2O3 carriers. Results show that the much superior catalytic properties of the developed Pt-Sn/Al2O3-mel catalyst compared to Pt-Sn/Al2O3-amm and Pt-Sn/Al2O3-com originate from the enhanced activation of propane by the electron-deficient characteristic of Pt by the intensified interaction of Pt/Sn and the facilitated mass transfer led by the unique morphology and surface properties of the carambola-like Al2O3-mel featuring opening structure.

Poly (triazine imide) (PTI) and graphene hybrids supported Pt[sbnd]Sn catalysts for enhanced electrocatalytic oxidation of ethanol

Rational design support materials are important for improving the efficiency of Pt-based catalysts. A series of PTI-graphene hybrids supported PtSn catalysts with different PTI nanosheets contents were synthesized by polyol method. Physical characterization revealed that PTI nanosheets can prevent restacking of graphene nanosheets and PtSn nanoparticles around 2.5 nm are dispersed uniformly on PTI-graphene support materials. Compared with the graphene supported PtSn catalyst and commercial carbon black supported Pt catalyst, the PTI-graphene hybrids supported PtSn catalysts exhibit excellent ultraefficient performance toward ethanol oxidation reaction (EOR). The enhanced electrochemical activity can be attributed to the high specific surface area of the PTI-graphene supports and the strong interaction between PtSn atom and supports as a result of the incorporation of PTI nanosheets.

Acetic acid hydrogenation to ethanol over supported Pt-Sn catalyst: Effect of Bronsted acidity on product selectivity

Gas phase hydrogenation of acetic acid was investigated over a series of SiO2-Al2O3 supported platinum-tin (Pt-Sn) catalysts. The active metals were impregnated over the support using incipient wetness technique and the resulting catalyst samples were characterized by Transmission electron microscopy, Hydrogen pulse chemisorption, BET surface area analyzer, Powder X-Ray diffraction, NH3-Temperature programmed desorption and H2-Temperature programmed reduction methods. Acetic acid hydrogenation reaction was carried out in an isothermal fixed bed catalyst testing unit. The results revealed that bimetallic Pt-Sn catalyst forms Pt-Sn alloy upon reduction which favors acetic acid hydrogenation to ethanol compared to competing side product CH4. The magnitude of Pt-Sn alloy formed per unit mass of catalyst depends upon the Pt/ Sn molar ratio in the calcined catalyst sample. 3 wt% Pt- 3 wt% Sn on SiO2-Al2O3 was found to be the optimum catalyst loading, resulting in 81% acetic acid conversion with 95% ethanol selectivity at 2 MPa and 270 °C. Further increase in ethanol selectivity would require prevention of esterification of acetic acid with ethanol, which leads to formation of ethyl acetate as by-product. The effect of catalyst acidity on acetic acid conversion and ethanol selectivity was studied and it was observed that proton donating capability of the support leads to the formation of ethyl acetate as by-product which, in turn, reduces ethanol selectivity. The ethanol synthesis reaction and esterification reaction over Bronsted acid sites takes place in series. The rate of esterification reaction was found to be highly dependent on the Bronsted acid density of the catalysts. Other catalyst parameters have little role on ethyl acetate yield.

Size effect of TS-1 supports on the catalytic performance of PtSn/TS-1 catalysts for propane dehydrogenation

Supported noble metal catalysts are extensively used for propane dehydrogenation in both the academy and industry. When the active components are fixed, the variation and improvement of the support will significantly affect the performance of the catalyst. Here we first prepared a series of PtSn/TS-1 catalysts with systematically controllable sizes of TS-1 zeolite supports. The particle sizes of the as-prepared TS-1 zeolite supports are from 100nm to 5.72μm. The TS-1 supports exhibited only weak acid sites, which avoids some side-reactions such as cracking and coking. The minimal size TS-1 (∼100nm)-supported PtSn catalyst gave the best catalytic performance and almost preserved the activity after a four-cycle reaction. The improved activity is ascribed to the hierarchically porous structure of the small-sized TS-1 sample, whereby diffusion hinders the mass transportation no more as certified by the Weisz–Prater criterion. The relationship between propane conversion and support size was fitted by a quadratic function. To further investigate the deactivation process, the species of deposited carbon was analyzed by in situ Raman methods. The work gave a new strategy for improving the catalytic performance of conventional supported catalysts in the PDH reaction, as well as some other heterogeneous catalysis.

Facile one-pot synthesized ordered mesoporous Mg-SBA-15 supported PtSn catalysts for propane dehydrogenation

A series of high-surface area and well-ordered mesoporous Mg-incorporated SBA-15 (xMg-SBA-15, x=0, 1, 2, 4 and 6) was prepared using a facile one-pot hydrothermal synthesis method. The resulting materials were used to disperse Pt, Sn particles and further studied the catalytic performance for propane dehydrogenation. The physicochemical properties of the supports and catalysts were characterized by XRD, N2 adsorption-desorption, FT-IR, TEM, NH3-TPD, XPS, H2-TPD and TG-DTA techniques. Compared with the sample synthesized by the impregnation method, the xMg-SBA-15 materials showed a better Mg species distribution and higher specific surface area. It was found that incorporation of appropriate amounts of Mg promoted the dispersion of metallic nanoparticles and facilitated the transfer of the carbon deposits from the active metal to the support. Such a modification of support not only enhanced the interaction of the Sn-support, but also stabilized the oxidation state of Sn species, leading to the improvement of catalytic activity and stability. The significant increases in conversion and selectivity were obtained on the modified catalysts with appropriate content of Mg. The best catalytic performances were obtained on PtSn/2Mg-SBA-15 catalyst with 2wt.% of magnesium, showing a higher than 98% selectivity toward propene at a 38.0% conversion of propane even after 6h reaction.

Hierarchical MgAl2O4 supported Pt-Sn as a highly thermostable catalyst for propane dehydrogenation

Highly thermal stability is an essential property for propane dehydrogenation (PDH) catalysts that need to be regenerated frequently in oxidative atmosphere. A kind of hierarchical MgAl2O4 with flower-like morphology is prepared by alcohothermal method and used to support Pt and Pt-Sn. The materials are characterized by ICP-AES, SEM, TEM, XRD, Py-IR, and N2 physi-sorption. Hierarchical MgAl2O4 supported Pt shows great thermal stability under oxidizing atmosphere at 800°C. Supported Pt-Sn catalyst for PDH shows high stability of performance during 10cycles of dehydrogenation-regeneration runs. The high stability could originate from the existence of relatively abundant MgAl2O4(111) facets on MgAl2O4.

Effect of Sn Addition in Gas Phase Hydrogenation of Acetic Acid on Alumina Supported PtSn Catalysts

Alumina supported Pt, Sn and PtSn catalysts were prepared by impregnation and tested in the gas phase hydrogenation of acetic acid, and characterized by N2-physisorption, XRD, H2-TPR, H2-pulse chemisorption, H2-TPD, DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy), XPS, electron microscopy techniques (TEM, HRTEM and EDX). Results show that Sn addition to Pt/Al2O3 catalyst can improve the conversion of acetic acid and suppress the production of by-products, as well as enhance the selectivity towards ethanol. The optimization of activity and selectivity can be achieved by changing reaction temperature and pressure. Characterizations indicated that the better performance of PtSn/Al2O3 catalyst is due to the formation of PtSn alloy and Pt-SnOx species.

Dehydrogenation of n-dodecane over Pt[sbnd]Sn/Mg[sbnd]Al[sbnd]O catalysts: Investigating the catalyst performance while monitoring the products

n-Dodecane was dehydrogenated over PtSn/MgAlO catalysts. Al2O3 and MgAlO supports with different Mg/Al mole ratio were prepared using a chemical co-precipitation method. The supports and supported PtSn catalysts were characterized using BET, XRD, CO-chemisorption, NH3-TPD, and TG. The dehydrogenation products were analyzed by GC. A single photon ionization time-of-flight mass spectrometer (SPI-TOF-MS) was developed and used to monitor the dehydrogenation products on-line during continuous reactions. Adding Mg to the supports decreased the specific surface area, increased the pore volume and diameter, moderated the acidity, and changed the strong acidic sites to weak ones. The dehydrogenation activity of the catalysts was inhibited, while the mono-olefin selectivity and yield were enhanced by Mg addition. Using a 1/3 Mg/Al molar ratio generated the optimal n-dodecene yield over the PtSn/MgAlO catalysts. The TOF-MS was reliable for detecting the dehydrogenation products of the long-chain paraffins rapidly, continuously, and accurately. Interestingly, TOF-MS can be used to monitor the reactions on-line and in situ, providing analyses of the products during high temperature reactions.

Novel BN supported bi-metal catalyst for oxydehydrogenation of propane

A novel boron nitride (BN) supported Pt-Sn catalyst was used for the oxydehydrogenation of propane. BN is a graphite-like inert support which provides negligible interaction with metals. The Pt-Sn/BN catalysts were prepared by co-incipient wetness impregnation with various Sn loadings. A commercial support γ-Al2O3 was chosen to compare with BN. PtSn alloys were formed due to the partially reduced Sn in Pt-Sn/BN catalyst in H2 at 400 °C. Furthermore, the crystalline phases of PtSn and SnPt3 alloys were also observed from the XRD patterns of Pt-Sn/BN catalysts. However, PtSn alloys were not detected in Pt-Sn/γ-Al2O3 by XRD. The Sn addition clearly improved the activity and propylene selectivity of Pt-Sn/BN at 600 °C. The more the Sn loading, the higher the selectivity and yield of propylene were. A maximum yield of propylene (38.3%) was achieved on Pt-Sn (0.75 wt%)/BN catalyst at the start of reaction. The catalysts, Pt-Sn/γ-Al2O3, deactivated more rapidly than Pt-Sn/BN. The activity and selectivity enhancement are attributed to the formation of PtSn and/or SnPt3 alloy particles on the BN support. Compared with the hydrophilic γ-Al2O3, the hydrophobic BN surface can expel H2O during the oxidation of hydrogen resulting in the activity increase.

Simultaneous HDS and HDN over supported PtSn catalysts in comparison to commercial NiMo/Al2O3

The performance of platinum-tin catalysts, supported on Al2O3 and SiO2 and subjected to reduction prior to use, has been studied. The catalysts were characterized in reduced forms by X-ray diffraction (XRD) and XPS. The surface properties were determined by N2 BET specific surface area and CO chemisorption. The model compounds were 4,6-dimethyldibenzothiophene (4,6DMDBT) and carbazole. The PtSn catalysts supported on either Al2O3 or SiO2 were characterised by high activity, but the catalyst PtSn/SiO2 was found the most effective, even more effective than the commercial KF848 catalyst. Both PtSn catalysts studied were more effective in the reaction of 4,6DMDBT hydrogenation, the dominant product obtained with the use of PtSn/Al2O3 was methyl-cyclohexyltoluene (MCHT) and with PtSn/SiO2 the dominant product was dimethylbicyclohexyl (DMBCH). The amount of dimethylbiphenyl (DMBPh) obtained was small and practically independent of the contact time. In the HDN reaction of carbazole the most active was PtSn/SiO2. It was also more active in the consecutive reaction of isomerisation of the main product of the HDN reaction, bicyclohexyl (BCH) to methylcyclopentylcyclohexane (MCPCH). The large differences shown in the hydrotreating activity specially in the HDN reaction between PtSn catalysts supported on Al2O3 and SiO2 result from the physicochemical properties of both samples. The significantly higher CO chemisorption for PtSn/SiO2 indicates the presence of larger amount of metallic species and better hydrogenation properties so important for deep hydrotreating process.

Mesocarbon microbeads supported PtSn catalysts for electrochemical oxidation of ethanol

Mesocarbon microbeads (MCMB) supported PtSn catalysts were prepared by alcohol reduction method and characterized by XRD, FESEM and EDX. XRD results show that the addition of Sn to Pt/MCMB extends the fcc lattice parameters of platinum and the particle size of PtSn/MCMB is about 2.6 nm, smaller than that of Pt/MCMB. The electrode catalytic activity in the electro-oxidation of ethanol was studied by cyclic voltammetry, Tafel plot, electrochemistry impedance spectra (EIS) and chronoamperometry. All the results showed that PtSn/MCMB gave higher catalytic activity for ethanol electro-oxidation than Pt/C (20 wt.% E-TEK).

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.

XPS and EXAFS study of supported PtSn catalysts obtained by surface organometallic chemistry on metals: Application to the isobutane dehydrogenation

In this work, well defined alumina and silica supported Pt and PtSn catalysts were prepared by surface organometallic reactions and were characterized by TEM, XPS and EXAFS. These catalysts were tested in the catalytic dehydrogenation of isobutane. XPS results show that tin is found under the form of Sn(0) and Sn(II,IV), being the percentage of Sn(0) lower for alumina supported than for silica supported catalysts. Tin modified platinum catalysts, always show a decrease of approximately 1 eV in the BE of Pt, what would be indicative of an electron charge transfer from tin to platinum. When the concentration of Sn(0) is high enough, in our case Sn(0)/Pt ∼ 0.3, EXAFS experiments demonstrated the existence of a PtSn alloy diluting metallic Pt atoms, for both PtSn/γ-Al 2O 3 and PtSn/SiO 2. This PtSn alloy seems to be not active in the dehydrogenation reaction; however, it is very important for selectivity and stability, inhibiting cracking and coke formation reactions. The ensemble of our catalytic, XPS and EXAFS results, show that bimetallic PtSn/γ-Al 2O 3 catalysts, prepared via SOMC/M techniques, can be submitted to several sequential reaction–regeneration cycles, recovering the same level of initial activity each time and that the nature of the catalytic surface remains practically without modifications.

Pt-based anode catalysts for direct ethanol fuel cells

In the present work, several carbon supported PtSn and PtSnRu catalysts were prepared with different atomic ratios and tested in direct ethanol fuel cells (DEFC) operated at lower temperature ( T=90 °C). XRD and TEM results indicate that all of these catalysts consist of uniform nano-sized particles of narrow distribution and the average particle sizes are always less than 3.0 nm. As the content of Sn increases, the Pt lattice parameter becomes longer. Single direct ethanol fuel cell tests were used to evaluate the performance of carbon supported PtSn catalysts for ethanol electro-oxidation. It was found that the addition of Sn can enhance the activity towards ethanol electro-oxidation. It is also found that a single DEFC of Pt/Sn atomic ratio≤2, “Pt 1Sn 1/C, Pt 3Sn 2/C, and Pt 2Sn 1/C’’ shows better performance than those with Pt 3Sn 1/C and Pt 4Sn 1/C. But even adopting the least active PtSn catalyst, Pt 4Sn 1/C, the DEFC also exhibits higher performance than that with the commercial Pt 1Ru 1/C, which is dominatingly used in PEMFC at present as anode catalyst for both methanol electro-oxidation and CO-tolerance. At 90 °C, the DEFC exhibits the best performance when Pt 2Sn 1/C is adopted as anode catalysts. This distinct difference in DEFC performance between the catalysts examined here is attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. It is thought that −OH ads, surface Pt active sites and the ohmic effect of PtSn/C catalyst determines the electro-oxidation activity of PtSn catalysts with different Pt/Sn ratios.

Direct ethanol fuel cells based on PtSn anodes: the effect of Sn content on the fuel cell performance

In the present work, several carbon supported PtSn catalysts with different Pt/Sn atomic ratios were synthesized and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Both the results of TEM and XRD showed that all in-house prepared carbon supported Pt and PtSn catalysts had nanosized particles with narrow size distribution. According to the primary analysis of XPS results, it was confirmed that the main part of Pt of the as-prepared catalysts is in metallic state while the main part of Sn is in oxidized state. The performances of single direct ethanol fuel cells were different from each other with different anode catalysts and at different temperatures. It was found that, the single DEFC employing Pt 3Sn 2/C showed better performance at 60 °C while the direct ethanol fuel cells with Pt 2Sn 1/C and Pt 3Sn 2/C exhibited similar performances at 75 °C. Furthermore, at 90 °C, Pt 2Sn 1/C was identified as a more suitable anode catalyst for direct ethanol fuel cells in terms of the fuel cell maximum power density. Surface oxygen-containing species, lattice parameters and ohmic effects, which are related to the Sn content, are thought as the main factors influencing the catalyst activity and consequently the performance of single direct ethanol fuel cells.

Composition-Size Diagrams of Supported Pt-Sn Catalysts

Composition-Size Diagrams of Supported Pt-Sn Catalysts

Reduction of Prostaglandin Unsaturated Ketones to Secondary Allylic Alcohols by Hydrogen Transfer over Mesoporous-Supported PtSn Catalysts

Supported PtSn catalysts were prepared by successive impregnation of SiO2, MCM-41, or MCM-48 materials with Pt and Sn, followed by calcination and reduction. The oxidation and aggregation state of the Pt and Sn were studied using combined temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy experiments. The characteristics of the bimetallic catalysts were related to the catalytic behavior in the hydrogen transfer reduction of the unsaturated ketone moiety in some intermediates of the prostaglandin synthesis; isopropanol was used as the reductant. High chemoselectivities to the allylic alcohol (over 95%) were obtained with catalysts containing 5 wt% Pt and 5–10 wt% Sn on MCM-41 or MCM-48. Characterization of these optimum catalysts evidenced that most of the Pt and part of the Sn form supported alloy particles with PtSn and PtSn2 composition; the rest of the Sn is present as dispersed Sn2+/4+. Activation of the carbonyl group on oxidized Sn, steric shielding of the CC bond by bulky substituents, and use of the hydrogen transfer donor seem crucial for obtaining high allylic alcohol chemoselectivities. In some cases, the mesoporous texture of the support induces significant diastereoselectivity, with one isomer of the secondary allylic alcohol prevailing over its epimer.

FTIR and XPS study of supported PtSn catalysts used for light paraffins dehydrogenation

A comparison between the characteristics of the metallic phase (studied by FTIR and XPS) of Pt and PtSn catalysts supported on Al2O3, K-doped Al2O3 and MgO (used for light paraffins dehydrogenation reactions) is reported in this paper. The beneficial effects produced by tin addition to platinum, both in the increase of the selectivity to propene and the low coke formation, would be related with the possible electronic modifications of Pt by Sn, with probable formation of alloys, mainly for Al2O3 and MgO supported bimetallic catalysts. On the other hand, the modification of the electronic state of Pt by Sn addition appears to be of a minor importance in bimetallic catalysts supported on K-doped Al2O3.