PtSn Catalysts Research Articles

Chemoselective hydrogenation of citral by Pt and Pt-Sn catalysts supported on TiO2 nanoparticles and nanowires

Chemoselective hydrogenation of citral is studied over platinum catalyst supported on titanium dioxide nanoparticles and nanowires. The support is found to have considerable effect on both selectivity and activity. Because of the presence of weak basic sites on the nanowire support, the platinum catalyst shows significantly higher activity and better selectivity towards citronellal than that obtained by the catalyst based on TiO2 nanoparticles having mainly medium strong basic sites. Furthermore, addition of tin promoter to the platinum catalyst decreases the initial rate of reaction and increases the selectivity towards unsaturated alcohols such as nerol and geraniol. The catalytic activity studies are complemented by chemical composition, surface adsorption and structural analyses of the applied catalyst materials assessed by the means of X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, temperature programmed reduction, H2 and CO2 desorption, CO chemisorption, electron microscopy and X-ray diffraction, respectively.

CO oxidation on PtSn nanoparticle catalysts occurs at the interface of Pt and Sn oxide domains formed under reaction conditions

The barrier to CO oxidation on Pt catalysts is the strongly bound adsorbed CO, which inhibits O2 adsorption and hinders CO2 formation. Using reaction studies and in situ X-ray spectroscopy with colloidally prepared, monodisperse ∼2nm Pt and PtSn nanoparticle catalysts, we show that the addition of Sn to Pt provides distinctly different reaction sites and a more efficient reaction mechanism for CO oxidation compared to pure Pt catalysts. To probe the influence of Sn, we intentionally poisoned the Pt component of the nanoparticle catalysts using a CO-rich atmosphere. With a reaction environment comprised of 100Torr CO and 40Torr O2 and a temperature range between 200 and 300°C, Pt and PtSn catalysts exhibited activation barriers for CO2 formation of 133kJ/mol and 35kJ/mol, respectively. While pure Sn is readily oxidized and is not active for CO oxidation, the addition of Sn to Pt provides an active site for O2 adsorption that is important when Pt is covered with CO. Sn oxide was identified as the active Sn species under reaction conditions by in situ ambient pressure X-ray photoelectron spectroscopy measurements. While chemical signatures of Pt and Sn indicated intermixed metallic components under reducing conditions, Pt and Sn were found to reversibly separate into isolated domains of Pt and oxidic Sn on the nanoparticle surface under reaction conditions of 100mTorr CO and 40mTorr O2 between temperatures of 200–275°C. Under these conditions, PtSn catalysts exhibited apparent reaction orders in O2 for CO2 production that were 0.5 and lower with increasing partial pressures. These reaction orders contrast the first-order dependence in O2 known for pure Pt. The differences in activation barriers, non-first-order dependence in O2, and the presence of a partially oxidized Sn indicate that the enhanced activity is due to a reaction mechanism that occurs at a Pt/Sn oxide interface present at the nanoparticle surface.

Insight into the Effect of Sn on CO and Formic Acid Oxidation at PtSn Catalysts

The role of Sn on the catalytic activity for CO and formic acid oxidation is studied by comparing the activities of differently treated PtSn/C and Pt/C catalysts. The catalysts are prepared by a microwave-assisted polyol synthesis method. As revealed by scanning tunneling and transmission electron microscopic (STM and TEM) characterization, the outcomes of the synthesis procedure for both Pt and PtSn are small particles, ∼1.5 nm in diameter. Upon deposition on the carbon support, the particle size increases to ∼2.5 nm due to sintering. X-ray diffraction (XRD) analysis shows that PtSn/C has a low alloying degree and is mainly composed of Pt and Pt3Sn phases. The remaining Sn is present in the form of very small tin oxide particles. Different surfaces are obtained by double-layer, oxide, and CO annealing of the Pt/C and PtSn/C catalysts and by modifying the CO-annealed surfaces with irreversibly adsorbed tin, Snirr. The presence of Sn in any form (oxide, alloyed, or Snirr) on the surface shifts the onset po...

Comparative study of bimetallic Pt-Sn catalysts supported on different supports for propane dehydrogenation

Bimetallic PtSn catalysts supported on different supports (ZSM-5, γ-Al2O3, mesoporous alumina, SBA-15) were prepared and several techniques were employed to study the influence of different supports on the catalytic structure and reaction performances. According to the results of XRD, textual properties and acid measurements for the as-prepared catalysts, the selected support is the main factor to determine the porous character and the acidic properties of the corresponding catalyst. In our experiments, when the used support is mesoporous alumina, most uniform and narrow distribution of metallic particles can be obtained. Furthermore, the presence of this support promotes the occurrence of spillover hydrogen and strengthens the interaction between Sn species and the support. As a result, the oxidative state of Sn can be stabilized and the transformation of active sites is promoted, thus improving the catalytic stability and reaction selectivity. Compared with this, the existence of the strong acid sites in ZSM-5 induces more cracking reaction and the porous character of γ-Al2O3 increases the accumulation of the coke. Meanwhile, the use of SBA-15 support leads to the agglomeration of metallic particles and the easy reduction of tin species, which is disadvantageous to the reaction.

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.

N-Decane dehydrogenation on Pt, PtSn and PtGe supported on spinels prepared by different methods of synthesis

The catalytic performance of Pt, PtSn and PtGe supported on ZnAl2O4 obtained by mechanochemical synthesis (MS) or coprecipitation (COPR) is studied in the production of 1-decene from the n-decane dehydrogenation. The effect of preparation methods and Sn and Ge addition to Pt on the activity and selectivity was analyzed. The catalytic characterization was carried out by using XRD, Specific surface area, 2-propanol dehydration reaction, equilibrium pH, cyclohexane dehydrogenation (CHD), cyclopentane hydrogenolysis (CPH), TPR, H2 chemisorption, XPS, TPO, and TEM. Characterization studies indicate that the addition of Sn to the Pt metal phase modifies not only the catalytic properties, but deactivation and stability as well. PtSn catalysts on both spinels were more active, with lower activity fall than PtGe ones and the higher the Sn loading, the more noticeable this effect. Besides, PtSn catalysts supported on ZnAl2O4 MS showed a more stabilizing effect.

Selective and stable bimetallic PtSn/θ-Al2O3 catalyst for dehydrogenation of n-butane to n-butenes

PtSn/θ-Al2O3 with various Pt and Sn compositions was prepared by a co-impregnation method using θ-Al2O3 support for n-butane dehydrogenation reaction. The monometallic Pt1.5/θ-Al2O3 catalyst showed severe deactivation in n-butane dehydrogenation. The bimetallic PtSn/θ-Al2O3 catalyst improved the n-C42− yield and the stability. The compositions listed in order of n-C42− yield at 823K are as follows: (PtSn)1.5>(PtSn)1.0>(PtSn)2.0>(PtSn)0.5>Pt1.5>Sn1.5. The n-C42− yields increased with the specific metal surface area. The Sn loading was varied on the Pt1.5 loaded catalyst. Then, the compositions listed in order of n-C42− yield at 823K were as follows: (PtSn)1.5>Pt1.5Sn1.0>Pt1.5Sn2.0>Pt1.5Sn0.5>Pt1.5. The n-C42− yield was maximized at a Pt/Sn weight ratio of 1.0. The n-C42− selectivity of the Pt1.5 catalyst was substantially improved by the Sn addition. TEM and XRD studies indicated PtSn alloy formation on the bimetallic PtSn catalysts during the reduction. The PtSn alloy can increase the n-C42− selectivity by blocking the cracking and hydrogenolysis sites of the Pt catalyst. TPR and HAADF STEM-EDS studies suggest the reduction procedure of the Pt and Sn species. The scattered Pt oxides in the vicinity of the well-dispersed Sn oxides were co-reduced, and then the reduced Sn metals migrated to the PtSn particles, resulting in a PtSn alloy. The specific metal surface area of the Pt1.5 sample was much lower than that of the (PtSn)1.5 sample. Therefore, it can be suggested that Pt metal sintering can be retarded by PtSn alloy formation during the reduction, resulting in high specific metal surface area. These observations demonstrate that the addition of Sn can enhance the activity and n-C42− selectivity.

Formation of different promoted metallic phases in PtFe and PtSn catalysts supported on carbonaceous materials used for selective hydrogenation

In this paper, a study on the selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols (UA) by using two series of PtSn and PtFe catalysts with different metallic loadings and supported on carbon nanotubes and carbon Vulcan is reported. The catalysts were prepared by conventional impregnation using the corresponding metallic precursors, H2PtCl6, SnCl2, and FeCl3. Once reduced under hydrogen flow, the supported catalysts were characterized by temperature-programmed reduction (TPR), H2 chemisorption, test reactions of the metallic phase, and X-ray photoelectron spectroscopy (XPS). Hydrogenation results show that the addition of a second metal to Pt leads to important modification of the selectivity, although the highest selectivities to UA are reached with very different Fe or Sn loadings. The performance of the catalysts in the citral hydrogenation was related to the characteristics of the bimetallic phase. It was found that the Fe addition to Pt catalysts results in a typical behavior such as for an usual ionic promoter in contact with the active metal, reaching high selectivities to UA as the Fe loading and the Fe ionic species percentage increases, while for PtSn catalysts, a high selectivity to UA was found only with a very low amount of Sn ionic species in contact with a very high percentage of Sn reduced species. The best selectivity to UA (about 98%) was found for PtSn(1wt%)/CN-P catalyst treated with N2 at high temperature.

Radiolytic Synthesis of Pt-M@MWNT Catalysts (M=Ru, Sn, and Au) for Biosensors

Non-enzymatic biosensors employing multi-walled carbon nanotube (MWNT) with highly dispersed Pt-M (M = Ru, Sn, and Au) nanoparticles (Pt-M@MWNT catalysts) were fabricated by radiolytic deposition. The Pt-M nanoparticles on the MWNTs were characterized by transmittance electron microscopy, elemental analysis, and X-ray diffraction. They were found to be well-dispersed and to exhibit alloy properties on the MWNT support. Electrochemical testing showed that these non-enzymatic biosensors had larger currents (mA) than that of a bare glassy carbon (GC) electrode and one modified with MWNTs. The sensitivity (μA mM-1), linear range (mM), and detection limit (mM) (S/N = 3) of the glucose biosensor with the Pt-Ru, Pt-Sn and Pt-Au catalysts in PBS electrolyte were determined, respectively. The experimental results show that such biosensors can be applied to glucose detection in food chemistry field.

Adsorption and oxidation of acetaldehyde on carbon supported Pt, PtSn and PtSn-based trimetallic catalysts by in situ Fourier transform infrared spectroscopy

The adsorption and oxidation of acetaldehyde on carbon supported Pt, Pt90Sn10 and Pt80Sn10M10 (M = Ni, Co, Rh, Pd) catalysts have been investigated by using in situ Fourier transform infrared (FTIR) spectroscopy. The result revealed that Pt90Sn10/C catalyst is not very efficient for the conversion of acetaldehyde to CO2 due to the weak adsorption of acetaldehyde in the presence of Sn. However, the addition of a third metal to Pt–-Sn facilitates the C–C bond cleavage of acetaldehyde. It seems that acetaldehyde is adsorbed dissociatively on the surface of Pt80Sn10Ni10/C, Pt80Sn10Co10/C, Pt80Sn10Rh10/C catalysts, producing CH3 and CHO adsorbate species, which can be further oxidized to CO2. However, the pathway forming CO2 for Pt80Sn10Pd10/C catalyst mainly originates from the oxidation of CH3CO species. Thus, the presence of third metal in the PtSn catalyst has a strong impact upon the acetaldehyde adsorption behaviour and its reaction products.

Impact of Organic Ligands on the Structure and Hydrogenation Performance of Colloidally Prepared Bimetallic PtSn Nanoparticles

AbstractThe catalytic performance of ligand‐capped monometallic Pt and bimetallic PtSn nanoparticles supported on SiO2 toward the selective hydrogenation of acetylene to ethylene in ethylene‐rich streams was investigated. To evaluate the effect of organic ligands on the hydrogenation performance, dodecylamine (DDA)‐capped monometallic and bimetallic nanoparticles were compared with ligand‐free nanoparticles. Both ligands and Sn promote the selectivity of the catalysts. The most selective catalyst was found to be the DDA‐capped PtSn catalyst, with a nominal metal atom ratio of 1:1. An increase in Pt content resulted in a decrease in the selectivity, whereas an increase in Sn content caused a decrease in the activity.

MgAl2O4 spinel prepared by mechanochemical synthesis used as a support of multimetallic catalysts for paraffin dehydrogenation

The catalytic performance in n-butane dehydrogenation of bimetallic PtSn, PtGa and PtIn, and trimetallic PtSnIn and PtSnGa catalysts (with low metal contents) supported on a MgAl2O4 prepared by a novel mechanochemical synthesis was evaluated both in flow and pulse equipment. The influence of the addition of different promoters (Sn, Ga and In) to Pt on the activity, selectivity and deactivation in the n-butane dehydrogenation reaction was studied. Stability experiments through successive reaction-regeneration cycles were carried out for selected catalysts. In order to correlate the properties of the metallic phase of the catalysts with the catalytic behavior, several characterization techniques were used, such as test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), TPR, XPS, H2 chemisorption and TEM. Bimetallic PtSn catalyst has a better catalytic behavior than PtIn and PtGa ones. For PtSnM (M: In or Ga) catalysts, whereas Ga addition to the bimetallic catalyst does not practically modify the dehydrogenation performance, the addition of In produces an increase of the activity and the selectivity to butenes. Characterization results indicate the presence of geometric effects for the PtSn catalyst, and geometric and electronic effects for PtIn and PtGa ones. For trimetallic catalysts, the presence of a close contact between Pt, Sn and In or Ga in both trimetallic catalysts was found, mainly due to geometric effects like blocking and dilution of the active sites by the promoters. In stability experiments, the trimetallic PtSnIn/MgAl2O4 catalyst clearly displays the best catalytic performance along reaction-regeneration cycles, though PtSnGa and PtSn catalysts also showed a very good behavior through the successive cycles. The characterization of these catalysts after cycles shows that their metallic phases are slightly modified along the cycles.

Structural aspects of PtSn/γ-Al2O3 catalysts prepared through surface-controlled reactions: Behavior in the water denitrification reaction

This research focuses on the controlled preparation and characterization of PtSn/γ-Al2O3 catalysts and their activity and selectivity in water denitrification by reduction of NO3− and NO2− ions with hydrogen. The bimetallic PtSn catalysts were active in the hydrogenation of both NO3− and NO2− and the amount of Sn added had a pronounced influence on the activity of the catalysts, being PtSn0.25 catalyst the one with the best performance. An explanation for this behavior is given in terms of the electronic and geometric effects that the addition of tin exerts on Pt.

Preparation and performance research of PtSn catalyst supported on carbon fiber for direct ethanol fuel cells

PtSn anode catalyst supported on carbon fiber was taken as the anode catalyst of the MEA. Commercial Pt/C as the cathode catalyst was used in MEA as the cathode catalyst. The Nafion 115 membrane was the proton exchange membrane of the MEA. MEA was fabricated by hot-pressing. The sing flat cell was assembled with the prepared MEA. The influences of temperature, ethanol concentration, rates of liquor and O2 were studied. The results showed that the performance of the fuel was better when the concentration of ethanol was 1.0 mol/L, the rate of liquor was 1.0 mL/min, the temperature was 80°C, and the rate of O2 was 100 mL/min, the maximum power density of the fuel reached about 18.2 mW/cm2.

Electrooxidation of ethanol on PtSn nanoparticles in alkaline solution: Correlation between structure and catalytic properties

Ethanol and carbon monoxide oxidation in alkaline media is investigated on a series of carbon-supported PtSn nanoparticles synthesized using a polyol reduction method. The PtSn electrocatalysts include two groups where one group is composed of disordered PtSn alloys and the other group composed of PtSn alloys intimately mixed with a SnOx phase. All catalysts were active during cyclic voltammetry experiments but the bi-phase PtSn+SnOx nanoparticles have significantly higher current densities at lower overpotentials compared to the pure alloy PtSn catalysts. During chronoamperommetry measurements all catalysts deactivated with time and only the bi-phase PtSnOx catalysts reached steady-state current densities after 3000s with all others deactivating continuously. Catalyst bulk and surface structure were correlated with the observed electrochemical performance in alkaline media demonstrating that ethanol electrooxidation in 1M KOH is more facile when electrocatalysst contain higher total amounts of both Pt and oxides. Alloying of Pt with Sn improves intrinsic, per Pt, catalytic activity and plausibly prevents Pt oxidation. Moreover, oxides decrease deactivation, possibly through improved CO or other intermediate adsorbate oxidation due to enhanced OH surface coverage.

First-Principles Calculations of Propane Dehydrogenation over PtSn Catalysts

Density functional theory calculations have been performed to investigate the effect of Sn on the catalytic activity and selectivity of Pt catalyst in propane dehydrogenation. Five models with different Sn to Pt surface molar ratios are constructed to represent the PtSn surfaces. With the increase of the Sn content, the d-band of Pt is broadened, which gives rise to a downshift in the d-band center on the PtSn surfaces. Consequently, the bonding strength of propyl and propylene on the alloyed surfaces is lowered. With the decomposition of the adsorption energy, the change in the surface deformation energy is predicted to be the dominant factor that determines the variation in the adsorption energy on the surface alloys, while on the bulk alloys the change in the binding energy makes a major contribution. The introduction of Sn lowers the energy barrier for propylene desorption and simultaneously increases the activation energy for propylene dehydrogenation, which has a positive effect on the selectivity toward propylene production. Considering the compromise between the catalytic activity and selectivity, the Pt3Sn bulk alloy is the best candidate for propane dehydrogenation.

Microwave-assisted polyol synthesis of carbon-supported platinum-based bimetallic catalysts for ethanol oxidation

High surface area carbon-supported Pt, PtRh, and PtSn catalysts were synthesized by microwave-assisted polyol procedure and tested for ethanol oxidation in perchloric acid. The catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning tunnelling microscopy (STM), TEM, and EDX techniques. STM analysis of unsupported catalysts shows that small particles (∼2 nm) with a narrow size distribution are obtained. TEM and XRD examinations of supported catalysts revealed an increase in particle size upon deposition on carbon support (diameter ∼ 3 nm). The diffraction peaks of the bimetallic catalysts in X-ray diffraction patterns are slightly shifted to lower (PtSn/C) or higher (PtRh/C) 2θ values with respect to the corresponding peaks at Pt/C catalyst as a consequence of alloy formation. Oxidation of ethanol is significantly improved at PtSn/C with the onset potential shifted for ∼ 150 mV to more negative values and the increase of activity for approximately three times in comparison to Pt/C catalyst. This is the lowest onset potential found for ethanol oxidation at PtSn catalysts with a similar composition. Chronoamperometric measurements confirmed that PtSn/C is notably less poisoned than Pt/C catalyst. PtRh/C catalyst exhibited mild enhancement of overall electrochemical reaction in comparison to Pt/C.

Aqueous phase hydrogenolysis of glycerol to bio-propylene glycol over Pt–Sn catalysts

PtSn supported on SiO2 obtained via surface organometallic chemistry techniques catalyzes hydrogenolysis of glycerol to obtain bio-propylene glycol (PG). Bimetallic catalysts with Sn contents between 0.1% and 1% wt were carefully prepared by selective hydrogenolysis of Sn(n-C4H9)4 on Pt. TEM, TPR, H2 and CO chemisorptions, and XPS studies have shown that tin selective deposition on the metallic phase is obtained. At 200°C under N2 or H2 pressure, the presence of tin increases drastically: both the selectivity and the activity of the glycerol conversion into PG. During 2h batch runs; it could be observed that PtSn catalysts with Sn/Pt ratio=0.2 showed the best performance (PG selectivity=59% and 83% under N2 and H2 pressure respectively). The increase in activity and selectivity could be explained by the presence of Sn+n species “acid Lewis sites” which would facilitate the C–OH adsorption and its subsequent C–O cleavage favoring the propylene glycol production.

Fabrication of Nonenzymatic Glucose Sensors Based on Multiwalled Carbon Nanotubes with Bimetallic Pt-M (M = Ru and Sn) Catalysts by Radiolytic Deposition

Nonenzymatic glucose sensors employing multiwalled carbon nanotubes (MWNTs) with highly dispersed Pt-M (M = Ru and Sn) nanoparticles (Pt-M@PVP-MWNTs) were fabricated by radiolytic deposition. The Pt-M nanoparticles on the MWNTs were characterized by transmittance electron microscopy, elemental analysis, and X-ray diffraction. They were found to be well dispersed and to exhibit alloy properties on the MWNT support. Electrochemical testing showed that these nonenzymatic sensors had larger currents (mA) than that of a bare glassy carbon (GC) electrode and one modified with MWNTs. The sensitivity (A mM−1), linear range (mM), and detection limit (mM) (S/N = 3) of the glucose sensor with the Pt-Ru catalyst in NaOH electrolyte were determined as 18.0, 1.0–2.5, 0.7, respectively. The corresponding data of the sensor with Pt-Sn catalyst were 889.0, 1.00–3.00, and 0.3, respectively. In addition, these non-enzymatic sensors can effectively avoid interference arising from the oxidation of the common interfering species ascorbic acid and uric acid in NaOH electrolyte. The experimental results show that such sensors can be applied in the detection of glucose in commercial red wine samples.

Platinum nano particles dispersed in alumina

We report the propane dehydrogenation behavior of catalysts prepared using wet impregnation method that immobilize Pt nano cluster on the alumina surface. The immobilization of the metal particles and their nano size dimensions were demonstrated by transmission electron microscopy. Selectivity to propylene for these catalysts is comparable to those obtained over industrial Pt catalysts, yet the resistance to deactivation by carbon poisoning is much greater for our catalysts. The deactivation behavior is more typical of traditionally prepared PtSn catalysts on γ-alumina than of catalysts supported onθ-alumina.