Presence Of Platinum Catalyst Research Articles

Enhanced gas sensing performance of ZnO and Pt-doped ZnO nanostructured films by chemical spray pyrolysis

This study focuses on the preparation and characterization of zinc oxide (ZO) and platinum-doped zinc oxide (Pt-ZO) nanostructured thin films using the chemical spray pyrolysis technique. Structural and morphological properties of the films were investigated via X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). To understand the semiconducting nature and carrier dynamics, UV-Vis spectroscopy, electrical conductivity measurements, and a static gas sensing system were employed. The films exhibited crystallization in the hexagonal wurtzite structure with a preferred orientation along the (002) plane. FESEM images revealed the presence of small bright particles, particularly abundant in the 5 wt% Pt-doped ZO thin film, indicating the presence of platinum catalysts. Electrical conductivity measurements confirmed the semiconducting nature of the films. Optical parameters such as band gap and absorption index were obtained from UV-Vis spectroscopy. Gas sensing performance towards liquefied petroleum gas (LPG) showed that the 5 wt% Pt-doped ZO thin film exhibited a high response (69.9) to a 50 ppm concentration of LPG at 350 °C. The gas response and recovery times were observed to be 8 s and 12 s, respectively. These results are attributed to interactions between LPG molecules and adsorbed oxygen species on the sensor surface. Platinum atoms on the oxide surface facilitate the formation of oxygen vacancies and the dissociation of oxygen molecules at low temperatures, leading to increased adsorption and reaction with LPG molecules. This results in significant changes in the sensor's resistance, thereby amplifying the sensor response. The findings demonstrate the potential of Pt-doped ZO thin films for practical gas sensing applications.

Molecular dynamics simulation of gasification technology to produce hydrogen from biomass at different initial pressures in the presence of platinum catalyst

Biomass is a renewable source of energy obtained from biological materials. Gasification technology is commonly used to produce hydrogen (H2) from biomass. This method is based on the partial oxidation of the input materials and their conversion into synthetic gas. After gasification, the biomass is converted into a gas consisting of H2, carbon monoxide (CO), carbon dioxide (CO2), and other compounds. This research investigates the number of H2 molecules (n(H2)) and CO molecules (n(CO)) in the basic structure at a temperature and pressure of 1 bar and 1800 K. Additionally, the effect of initial pressure (IP) changes on the n(H2) and n(CO) produced with a 10 % volume fraction of platinum (Pt) catalyst was evaluated using molecular dynamics (MD) simulation. The results demonstrate that the produced n(H2) and n(CO) increase from 559 to 146 to 586 and 165, increasing the Pt nanocatalyst ratio from 1 % to 10 %. Furthermore, the n(H2) and n(CO) increase from 586 to 165 to 598 and 175, respectively, by increasing the IP from 1 to 5 bar. Also, the results reveal that the combustion efficiency (CE) increases from 62 % to 66 % with increasing IP from 1 to 5 bar. The application of this research is to study the production of hydrogen and carbon monoxide from biomass using gasification technology. This information can be useful for improving the efficiency of biomass gasification for hydrogen production.

Application of nonthermal atmospheric‐pressure plasma irradiation as a new method for noncatalytic liquid‐phase selective oxidation of polyhydric alcohols

AbstractWe have developed a new liquid‐phase noncatalytic selective oxidation of polyhydric alcohols such as glycerol. This method involves the use of a nonthermal atmospheric‐pressure plasma instead of precious‐metal catalysts. We found that noncatalytic selective oxidation of glycerol achieved a conversion comparable to that achieved by gold‐catalyzed oxidation, and the desired glyceric acid, which is a pharmaceutical raw material, was obtained. When the solution pH was changed from strongly alkaline to neutral, the main reaction switched from the one that occurs in the presence of gold catalysts to the one that occurs in the presence of platinum catalysts. These results suggest that the reactive oxygen species generated by nonthermal atmospheric‐pressure plasma irradiation vary depending on the solution pH.

Silane‐Bearing Borasilsesquioxanes: Synthetic Protocol and Unsuspected Redistribution Reactions

The presented work is a continuation of research on the reactivity of unsaturated borasilsesquioxanes under the conditions of common organometallic transformations. The catalytic hydrosilylation reaction with silanes, siloxanes and silsesquioxanes in presence of platinum catalyst was explored. The majority of the products were obtained in high yields (>90 %) and their structures were confirmed and characterized by spectroscopy and spectrometry, i. e. NMR and MALDI-TOF-MS. The most significant segment of the work is research on the spontaneous redistribution reaction of the alkoxy group from silane to borane moiety occurring in the obtained products, not being limited to the heterosilsesquioxane chemistry, however. The products were confirmed using GC-MS, ESI-MS methods and B3LYP exchange-correlation, in order to ascertain formation of the silicon-boron hybrid molecule.

Studies on the kinetics of catalytic combustion of deuterium using 0.5% platinum loaded on Dixon ring catalyst

When hydrogen isotopes are present in stoichiometric ratio of 2:1 with oxygen in inert gas such as helium, catalytic combustion is the most promising option to reduce the concentration of hydrogen isotopes and to minimize the associated safety hazards. This is the case, when deuterium and oxygen is formed during radiolysis of heavy water in moderator circuit of Pressurized Heavy Water Reactors (PHWR) and mixed with helium in the cover gas system. In order to design the catalytic reactor for recombination of deuterium and oxygen, the data on catalytic combustion kinetics under the similar process conditions are essential. However, the catalytic combustion data is generally reported for combustion of hydrogen in air, where oxygen is available in excess. The studies on the kinetics of catalytic combustion of deuterium where oxygen is present in stoichiometric ratio of 2:1 in an inert gas medium such as helium, is very scarce. In the present study, the multi-step reaction mechanism of catalytic combustion of hydrogen in presence of platinum catalyst is analyzed for the present process conditions. Based on the analysis, a simple rate expression is proposed for the present process conditions of catalytic combustion of deuterium. Further, 0.5% platinum catalyst is prepared on a stainless steel Dixon ring support with an objective to achieve better heat transfer characteristics and lesser reduction in the catalytic activity due to water adsorption. The kinetic data is generated using a differential packed bed reactor operating in a closed loop. The experiments were conducted at different temperatures using a stoichiometric mixture of deuterium and oxygen in helium. The rate constant for the above proposed model is estimated based on the experimental data at different temperatures. Further, the activation energy and frequency factor are determined and the activation energy for the present catalyst is found to be on the lower side in comparison to literature data.

β-Hydrosilylation of Allylic Derivatives with Cyclic and Linear Siloxanes in the Presence of Platinum Catalysts

The aim of this work is to study the influence of the nature and position of substitution at allyl benzene on the regioselectivity of the hydrosilylation reaction. We studied hydrosilylation of the various allyl derivatives with cyclic siloxane, D4H, and linears hydrosilylating agents, 1,1,3,3-tetramethyldisiloxane and MDHM, in the presence of platinum-based catalysts (Karstedt catalyst, platinum black). We also show the effects of the amount of catalyst on the conversion. Moreover, the influence on the temperature on catalytic activity and selectivity of the hydrosilylation reaction was explained. All new compounds were characterized by 1H, 13C, 29Si NMR and HRMS as well.

Assessment of Silicone Rubber Properties Using Dynamic Modelling Simulation

The investigation of silicone rubber properties with the presence of platinum catalyst at different temperature using molecular dynamic simulation was conducted. Visual observation shows that structuring of silicone rubber occurs in the cell where the molecules aggregates closer compared to at the beginning of the simulation and at higher platinum concentration, silicone rubber molecules are more closely packed together. The diffusion coefficient of silicone rubber are the highest in a 10% platinum concentration followed by 25% and lastly 50% indicating that it is harder for the silicone rubber molecules to move from its original position in the system as the platinum concentration increases. Structural changes was also investigated through radial distribution function (RDF) where the position of peaks did not change with time but there is changes observed in the intensity of the peak. At a constant temperature 50°C, it was observed that the intensity of the peak at 1.10Å radius was the highest in the presence of 50%Pt followed by 25%Pt and 10%Pt. This indicates that higher numbers of silicone rubber molecules are present in a 1.10Å radius from the reference molecules in a system with higher concentration of platinum.

Monolayer formation of luminescent germanium nanoparticles on silica surface in aqueous buffer solution.

The present paper reports monolayer formation of germanium nanoparticles (Ge NPs) on silica substrate. The NPs were prepared by hydride reduction of GeCl4, which is encapsulated with an inverse micelle of dimethyldioctylammonium bromide, with lithium aluminum hydride, and subsequent hydrogermylation of allylamine in the presence of platinum catalyst. The resultant NPs showed the blue photoluminescence property. Due to the terminal amine, the NPs were soluble highly in aqueous buffer solution. To fabricate a monolayer of Ge NPs, the chemical reactivity of the NPs was studied using a multi-functional microarray in which different kinds of siloxane monolayers were periodically aligned on a silica substrate. We observed using fluorescence microscope whether the terminal amines of the NPs recognize the specific monolayers in the microarray. In terms of fluorescence observation, the entire surface of the monolayer-covered microsize-domains emits uniformly the blue light. This suggests a high degree of coverage of the luminescent NPs covering over the monolayer regions in the microarray, and implies the non-occurrence of quenching through energy transfer between adjacent NPs.

Organomodified Silicone Elastomer (OMSE) for Next Generation Personal Care Products

Personal care (PC) products containing commercial silicone elastomer (SE) blends offer superior sensory, due to their silky and non-greasy characteristics. These products contain functional organic actives; namely sunscreens, antibacterial agents and dyes. The functional performance of the PC products is determined by the extent of deposition of the actives on the skin or hair. However, this performance is limited due to incompatibility of organic actives with the silicone elastomer (SE) blend. This review described recent development of organomodified silicone elastomers (OMSE) for enhanced compatibility and superior deposition of actives on the skin or hair. OMSEs contain covalently linked functional actives to the cross-polymeric silicone backbone. OMSE were synthesized by reacting alkenyl functional derivatives of avobenzone, benzylidene malonate, curcumin or hydroxyanthraquinone, suitable crosslinker, solubilizing (e.g. CnH2n i.e. alkyl) / emulsifying agents (e.g. polyether) with the poly(dimethyl)-co-(methylhydrogen)siloxane copolymer in the presence of platinum catalyst. OMSE showed superior functional performance due to uniform molecular distribution of sunscreen / dye molecules on the substrate surface. Covalently attached sunscreen / dye molecules on the cross-polymeric silicone backbone would show enhanced safety profile due to negligible possibility of penetration through skin.

Ultra-fast surface hydrophobic modification of sol–gel silica antireflective coating with enhanced abrasion-resistance

A novel and ultra-fast route was proposed to modify the surface hydrophobicity of sol–gel silica antireflective (AR) coating with poly(methylhydrogen)siloxane (PMHS). The hydroxyl groups on silica particle are thought to react with the hydrogen atoms within several seconds at room temperature in the presence of platinum catalyst. The surface modification can be accomplished simply by immerging silica AR coating into the PMHS/hexane solution containing platinum catalyst and then withdrawing immediately from the solution. The hydrophobicity and abrasion-resistance of PMHS modified AR coating were significantly improved. This provides a new method for the preparation of abrasion-resistant sol–gel silica AR coating used in outdoor environment.

Synthesis and Properties of Polysilsesquioxanes Having Ethoxysulfonyl Group as a Side Chain

Polysilsesquioxane having an ethoxysulfonyl group as a side chain was synthesized to prepare a proton-conductive film composed of a main chain of siloxane. At first, sodium 4-(2-methylallyloxy)benzenesulfonate was chlorinated with thionyl chloride. Next, hydrosilylation with trichlorosilane was carried out in the presence of platinum catalyst followed by treatment with ethanol. Finally, the hydrolytic polycondensation was carried out to provide poly(3-(4-ethoxysulfonylphenoxy)-2-methylpropyl)silsesquioxane. This polysilsesquioxane was heated to form a free-standing film that was brittle and brown in color.

Liquid Silicone Rubber Vulcanizates: Network Structure - Property Relationship and Cure Kinetics

Liquid silicone rubber (LSR) vulcanizates have been prepared from vinyl-end capped polydimethylsiloxane (PDMS) and polymethylhydrogenosiloxane (PMHS) in presence of platinum catalyst using solution casting technique. The science involving synthesis of usable silicone rubber by curing with polymethylhydrogenosiloxane has been studied in details. The effects of vinyl content of PDMS and the ratio of hydride crosslinker to vinyl concentration on crosslink density, mechanical, dynamic-mechanical and thermal properties have been discussed. It has been found that at optimum level of crosslinker, the LSR vulcanizate shows a maximum crosslink density with highest improvement in mechanical and thermal properties. The amount of crosslinker required, depends upon the number of vinyl functionality per unit length of the polymer chain and the chemical composition of the hydride crosslinker. This study makes a novel attempt to determine cure kinetics of PDMS by using Fourier Transform Infrared spectroscopy. Measurements have been done at three different temperatures and found to follow the first order reaction with respect to consumption of vinyl (C=C) and silyl hydride groups (Si-H). The activation energy and kinetic parameters have been determined as well.

Facile route to synthesis of functionalised poly(methylalkoxy)siloxane under mild and aerobic conditions in the presence of platinum catalysts

A facile and high yield method of synthesis of novel and functional poly(methylalkoxy) siloxanes is reported. The Si–H groups of poly(methylhydrogen) siloxanes (PMHS) were treated with various simple (primary, secondary, tertiary) alcohols (1a–10a) in the presence of platinum based catalysts (Speier’s and Karstedt’s catalysts). Also oxyethylene, aldehyde, epoxide, halogen and allyl grafted polysiloxane were smoothly and quantitatively prepared by the alcoholysis between linear siloxanes polymer and functional alcohols (11a–20a) with use of Karstedt’s catalysts. It is found that alcoholysis reaction in the presence of the Karstedt’s catalyst proceed faster than Speier’s catalyst .In addition, the rate of alcoholysis reaction is dependent on amount of the catalyst and reaction temperature. The polymers prepared were characterized by IR, NMR spectroscopy and GPC analysis.

Synthesis of [m,7,n]-Tricycles via Platinum-Catalyzed Cyclization of Conjugated Enynals with a Pendant Alkene

Conjugated enynals anchored to cycloalkenes, in the presence of platinum catalysts, were cyclized to the corresponding [m,7,n]-tricarbocycles, which are valuable skeletons in biologically active natural products like taxoids.

Preparation and properties of polyethoxysilsesquioxane‐C60 hybrids

AbstractFree‐standing films of C60‐polyethoxysiloxane hybrids were prepared, and their optical limiting properties were evaluated. Triethoxysilylated C60, with a formula of H3C60[Si(OEt)3]3, was synthesized by the hydrolysilylation of C60 with triethoxysilane in the presence of platinum catalyst. C60‐polyethoxysiloxanes were prepared by a cohydrolytic polycondensation of triethoxysilylated C60 with tetraethoxysilane in a molar ratio of Si/C60 = 10–1000 under nitrogen flow. The molecular weight of C60‐polyethoxysiloxane increased with a decrease of Si/C60. Transparent and flexible free‐standing films were prepared by aging an ethanol solution of C60‐polyethoxysiloxane at 80 °C for 6–8 days. The mechanical strength and Young's modulus increased with a decrease in Si/C60. These free‐standing films showed an optical limiting property, for which the threshold value decreased from 1163 mJ/cm2 (Si/C60 = 1000) to 130 mJ/cm2 (Si/C60 = 10) with a decrease of Si/C60. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3273–3279, 2007

Precise Synthesis of Poly(silphenylenesiloxane)s with Epoxy Side Functional Groups by Tris(pentafluorophenyl)borane as a Catalyst

1,ω-Dimethylhydroxysilyl, -dimethylhydrosilyl, -dimethylmethoxysilyl -terminated tetramethylsilphenylenesiloxane prepolymers were prepared by sequential palladium-catalyzed dehydrocoupling polymerization of 1,4-bis(dimethylsilyl)benzene with water, reduction with lithium aluminium hydride, and palladium-catalyzed methanolysis. 1,4-Bis[(glycidyl- or cyclohexene oxide-functionalized alkyl)methylhydrosilyl]benzene and methyldimethoxysilanes with the same epoxy groups were synthesized by hydrosilylation of 1,4-bis(methyldihydrosilyl)benzene and methyldimethoxysilane with (terminal olefin-functionalized alkyl) substituted epoxides in the presence of platinum catalyst. 1,4-Bis[(glycidyl- or cyclohexene oxide-functionalized alkyl)methyl(hydroxy or methoxy)silyl]benzenes were obtained by hydrolysis and methanolysis of the hydrosilyl derivatives. Poly(silphenylenesiloxane)s with epoxy side groups were synthesized by hetero-polycondensation of the hydrosilane, hydroxysilane and methoxysilane functional groups in the prepolymer and 1,4-bis[(epoxy-functionalized alkyl)methylsilyl]benzene, or 1,1-dimethoxy(epoxy-functionalized alkyl)methylsilane in the presence of a catalyst. Tris(pentafluorophenyl)borane was found to be an excellent catalyst for the polymerization. Cross-linking a polymer with 1,4-diaminobenzene gave stretchable polymer film by solution cast method.

Catalytic reactions of hydrosiloxanes with allyl chloride

Catalytic reactivity of Si–H bond of di-, trisiloxanes with allyl chloride in the presence of platinum catalyst has been examined. Hydrosilylation process competes with hydrogen substitution by chlorine and/or propenyl group. The effect of the reaction conditions as well as structure of siloxane on the yield and selectivity of the number of products has been discussed. Several consecutive-competitive processes have been identified. The results obtained can be helpful in the study of the catalytic hydropolysiloxanes reactions with allyl derivatives–systems of great practical importance, to produce commercial functionalized silicones.

Platinum‐Catalyzed Highly Selective Thiocarbonylation of Acetylenes with Thiols and Carbon Monoxide.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Platinum-catalyzed highly selective thiocarbonylation of acetylenes with thiols and carbon monoxide

A novel carbonylative addition of thiols (RSH) to terminal acetylenes (R′–CCH) takes place successfully in the presence of platinum catalysts under the pressure of carbon monoxide, providing α,β-unsaturated thioesters (R′–C(C(O)SR)CH 2) in good yields regioselectively. This ‘hydrothiocarbonylation’ reaction of acetylenes may include the formation of the platinum sulfide complex as key species.

Preparation of C60-silica hybrid monolith by sol-gel process

A C60–silica hybrid monolith was prepared by the hydrosilylation of C60 in the presence of platinum catalyst followed by sol-gel process with tetraethoxysilane. The hydrosilylation with trichlorosilane, triethoxysilane, chlorodiphenylsilane, and dichlorophenylsilane gave silylated C60s as a brown pasty liquid. The formula was estimated to be C60{Si(OEt)3}2.6H2.6 or C60(SiPh2Cl)3.2H3.2 based on the proton nuclear magnetic resonance spectrum. A C60–silica hybrid gel monolith was obtained by sol-gel process of the silylates and tetraethoxysilane in ethanol followed by aging for 3 weeks at room temperature. The monolith was brown and transparent with a diameter of 25 mm. On the other hand, the sol-gel reaction of tetraethoxysilane, trimethoxyphenylsilane, and C60 provided a heterogeneous gel with a phase separation of C60.