Nanophase Reactor Research Articles

Hydroformylation of dihydrofurans catalyzed by rhodium complex encapsulated hexagonal mesoporous silica

HRh(CO)(PPh3)3 encapsulated hexagonal mesoporous silica (HMS) is found to be an efficient heterogeneous catalyst for the selective hydroformylation of 2,3-dihydrofuran (2,3DHF) and 2,5-dihydrofuran (2,5DHF). The Rh-complex encapsulated in situ in the organic phase of template inside the pores of HMS was found to act as nano phase reactors. Conversion of 2,3-DHF and 2,5-DHF and selectivity of the corresponding aldehydes were thoroughly investigated by studying the reaction parameters: catalyst amount, substrate concentration, partial as well as total pressure of CO and H2, and temperature. The selectivity for the formation of tetrahydrofuran-2-carbaldehyde (THF-2-carbaldehyde) from the hydroformylation of 2,3-DHF was found to be more than the selectivity of the formation of tetrahydrofuran-3-carbaldehyde (THF-3-carbaldehyde) from 2,5-DHF. The reaction paths are suggested and discussed for the selective formation of the corresponding aldehydes. The catalyst was elegantly separated and effectively recycled for six times.

Hydroformylation of propene heterogeneously catalyzed by HRh(CO)(PPh 3) 3 encapsulated in to hexagonal mesoporous silica—Parametric variation and mass transfer study

An in situ encapsulated HRh(CO)(PPh 3) 3 in to the pores of hexagonal mesoporous silica (HMS) acting as nanophase reactors, was investigated for the catalytic hydroformylation of propene. The encapsulated catalyst (Rh–HMS) was synthesized and characterized by PXRD, FT-IR, surface area measurements and TEM. The catalyst was effectively active with 99% conversion of propene and 100% selectivity to aldehydes. The effects of reaction parameters: temperature, partial pressure of CO and H 2, amount of catalyst and HRh(CO)(PPh 3) 3 to TEOS ratio on conversion, selectivity and rates were investigated in detail. The rates determined in term of the formation of aldehydes were found to be first order with respect to hydrogen pressure. Catalyst showed first order dependence towards its lower amount. CO pressure variation showed positive order towards lower pressure and inhibition at higher pressures. The investigated mass transfer effects on the kinetics indicated that the reaction runs with negligible mass transfer limitations. The heterogenized Rh–HMS catalyst was effectively recycled for six times.

HRh(CO)(PPh 3) 3 encapsulated mesopores of hexagonal mesoporous silica (HMS) acting as nanophase reactors for effective catalytic hydroformylation of olefins

The rhodium complex HRhCO(PPh 3) 3 encapsulated into the pores of hexagonal mesoporous silica (HMS) by in situ synthesis (Rh–HMS) was found to be an efficient heterogeneous catalyst for the hydroformylation of C 5–C 12 olefins. The (Rh–HMS) catalyst system was thoroughly characterized by P-XRD, 31P CP-MAS NMR, FT-IR, TGA, SEM and N 2 adsorption/desorption techniques. The 31P CP-MAS NMR spectrum of Rh–HMS shows that the HRhCO(PPh 3) 3 complex encapsulated into the pores of HMS without decomposition, indicating that the pores of the catalyst system act as nanophase reactors. The detail investigations were performed on the effects of temperature, amount of catalyst, partial pressure of CO and H 2 and weight ratio of HRh(CO)(PPh 3) 3 to TEOS for the hydroformylation of 1-hexene. At lower temperature the selectivity and n/iso ratio of aldehydes was higher. The selectivity and n/iso ratio of aldehydes was increased on increasing the amount of HRhCO(PPh 3) 3 complex into the HMS. The catalyst had shown good thermal stability and recyclability. The catalyst was recycled giving excellent conversion (100%) for the hydroformylation of 1-hexene.

The effect of nanoparticle growth on rheological properties of silica and silicate dispersions

CdS and ZnS nanoparticles were prepared in the solid–liquid interfacial adsorption layer as a nanophase reactor. The substrates were hydrophilic and hydrophobic aerosils and hydrophilic layer silicates dispersed in ethanol–cyclohexane mixtures. The growth of particles at various surface concentration of precursor ions was monitored by absorption spectroscopy, band-gap-energy measurements and particle diameter measurements. Also, the rheological properties of nanoparticle–support composites in organic and aqueous dispersions were measured. The energy of separation between the nanoparticles depended on the particle diameter. The intercalation of nanoparticles in the layered silicates yielded a nanostructured two-phase system. The presence of semiconductive subcolloids was proven by transmission electron microscopy measurements, which offer an excellent possibility for the determination of the particle size distribution.

CdS, TiO 2 and Pd° nanoparticles growing in the interlamellar space of montmorillonite in binary liquids

The interfacial layers on the clay mineral/liquid interface usually range from 0.5 to 5 nm. When clay mineral particles are dispersed in binary mixtures (ethanol–cyclohexane and ethanol–toluene), an adsorption layer evolves on their surface which may function as a nanophase reactor for the synthesis of nanocrystalline materials. In the adsorption layer on the surface of montmorillonite CdS, TiO 2 and metallic palladium nanoparticles with a diameter of 5–15 nm were grown. The appearance of semiconductor particles and the dependence of particle size upon the Cd 2+ precursor concentration were followed by determination of the band gap energy. The rheological characteristics of suspensions containing nanoparticles are basically different from those of the original suspension. Solid powder samples obtained from the suspensions were studied by small-angle X-ray scattering (SAXS) measurements; the size of nanoparticles located on the clay mineral surfaces was determined and changes in the structure of the support were monitored.

Preparation of semiconductor and transition metal nanoparticles on colloidal solid supports

When colloid particles are dispersed in binary mixtures, an adsorption layer evolves on their surface which may function as a nanophase reactor for the synthesis of nanocrystalline materials. In the adsorption layer on the surface of ceramics (SiO 2, clays and layer double hydroxide, (LDH)), CdS, ZnS and metallic palladium nanoparticles with a diameter of 5–30 nm were grown. The appearance of semiconductor particles and the dependence of particle size upon Cd 2+ or Zn 2+ precursor concentration were followed by determination of a band gap energy. The rheological characteristics of suspensions containing nanoparticles are basically different from those of the original suspension. Solid powder samples obtained from the suspensions were studied using SAXS measurements; the size of nanoparticles located on ceramic surfaces was determined and changes in the structure of the support were monitored.

Preparation and hydrogen sorption of Pd nanoparticles on Al 2O 3 pillared clays

Pd nanoparticles were prepared in the solid–liquid adsorption layer on pillared clays and the subcolloids with a diameter of 3–5 nm obtained were characterized by various methods. Based on the liquid sorption isotherms determined in ethanol–toluene mixtures, the composition of the interfacial layer as a “nanophase reactor” may be determined; equilibrium conditions for the formation of Pd nanocrystals were selected. The surfacial binding of Pd 0 particles may be monitored by spectrophotometry throughout the preparation. N 2 adsorption measurements indicate a gradual decrease in micropores and external surface areas with increasing Pd content of the samples. According to TEM pictures, samples with higher Pd contents contain particles with larger diameters. These results are supported by SAXS and H 2 adsorption measurements as well. The relationship between catalytic activity and size of Pd subcolloids is revealed by microcalorimetric monitoring of hydrogen adsorption and by the results of catalytic hydrogenation reactions. These measurements indicate that smaller particles have larger catalytic activities.

In SituGeneration of Palladium Nanoparticles in Smectite Clays

A novel synthetic route has been developed for the preparation of clay intercalated palladium catalysts. Liquid sorption and X-ray diffraction measurements on ethanol(1)–toluene(2)/hexadecylammonium montmorillonite dispersions indicated that a toluene-rich bulk liquid phase was equilibrated with a swollen, ethanol-rich interlamellar phase having a volume of about 0.9 cm3/g organoclay. Introduction of palladium(II) acetate into the organoclay suspension led to the generation and deposition of a metallic palladium dispersion in the interlamellar space. This system behaved as a versatile nanophase reactor, wherein the ethanol functioned as both solvent and reducing agent. The progress of the Pd2+→Pd0reaction was monitored spectrophotometrically. The ethanolic reduction afforded Pd particles 2 to 14 nm in diameter, depending on the experimental conditions, deposited on clay particle defect sites. Organoclays loaded up to 10 mass% Pd were synthesized and characterized by BET surface area analysis, transmission electron microscopy, low-shear rheology, X-ray diffraction, and small-angle X-ray scattering measurements. The Pd–organoclay samples proved to be cata?-lytically active in olefin hydrogenation in the liquid phase.

Preparation and Characterization of CdS and ZnS Particles in Nanophase Reactors Provided by Binary Liquids Adsorbed at Colloidal Silica Particles

Determinations of adsorption excess isotherms of silica particle dispersions in ethanol−cyclohexane and in methanol−cyclohexane binary mixtures have established the formation of 0.5−5.0 nm thick alcohol rich adsorption layers at the silica particle interface. The adsorption layers on silica particles, formed in methanol−cyclohexane = 0.01:99.99 (mol/mol) and ethanol−cyclohexane = 0.05:99.95 (mol/mol), were used as nanophase reactors for the in situ generation of size-quantized CdS and ZnS particles. The semiconductor particles were generated by the addition of H2S to silica particle dispersions which contained different concentrations of Cd2+ or Zn2+. The smallest semiconductor particles were generated in dispersions which contained the least amount of precursors. Absorption spectrophotometry, small-angle X-ray scattering, rheological, and calorimetric measurements were used to characterize the dispersions. The presence of semiconductor particles increased the viscosities and decreased the immersion wetting enthalpies of the silica dispersions, indicating strong interparticle interactions.

Preparation of Size-Quantized CdS and ZnS Particles in Nanophase Reactors Provided by Binary Liquids Adsorbed at Layered Silicates

Liquid sorption measurements of hexadecylpyridinium montmorillonite (HDPM) dispersions in ethanol (1)-cyclohexane (2) and methanol (1)-cyclohexane (2) binary mixtures established the formation of a 0.5- to 5-nm-thick alcohol (1)-rich adsorption layer at the organoclay complex interfaces. This adsorption layer was used as a nanophase reactor for the in situ generation of size-quantized cadmium sulfide and zinc sulfide semiconductor particles from cadmium (or zinc) acetate and equivalent amounts of H 2 S. The volumes of the nanophase reactor in ethanol (1)-cyclohexane (2) at 1 :2 = 0.05 :99.95 were determined, by adsorption excess isotherm and X-ray diffraction measurements, to be 0.692 cm 3 /(g of HDPM) and 0.746 cm 3 /(g of HDPM), respectively. Adsorption excess isotherm and X-ray diffraction measurements gave corresponding values of 0.170 cm 3 /(g of HDPM) and 0.231 cm 3 /(g of HDPM) in methanol (1)-cyclohexane (2) at 1 :2 = 0.01 :99.99. As expected, smaller sized semiconductor particles were generated in the smaller nanophase reactor, provided by the methanol-rich adsorption layer. Further reduction of semiconductor particles was accomplished by decreasing the concentration of their parent ions in the nanophase reactor. Incorporation of semiconductor nanocrystallites into HDPM manifested themselves in increased viscosity of the suspension. Information on the fractal dimensions of the semiconductor-clay organocomplex suspensions and that on the radius of gyration of the nanoparticles has been determined by small-angle X-ray scattering measurements. The use of selectively adsorbed polar liquids at the solid binary polar-apolar liquid mixture interfaces as versatile nanophase reactors is discussed.