Igor Yuranov

Pd/SiO2 catalysts: synthesis of Pd nanoparticles with the controlled size in mesoporous silicas

Synthesis of Pd nanoparticles with controlled size (d(Pd) = 1-3.6 nm) was carried out within the pores of the mesoporous HMS and SBA-15 silicas. Pd was ion-exchanged on non-calcined silicas, prepared by solvent extraction of the templates. A high concentration of silanol groups on the mesopore surface allowed attaining Pd loading up to 4.4. wt.%. The Pd/HMS and Pd/SBA-15 were characterised by chemical analysis, XRD, N2 adsorption-desorption and transmission electron microscopy (TEM) methods. The materials possess a high SSA and narrow pore size distribution. Introduction of Pd nanoparticles in HMS resulted in a progressive loss of the regularity in the mesoporous structure. On the contrary, all Pd/SBA-15 composites retained the original well-ordered 2D hexagonal structure of SBA-15. The thick walls of the SBA-15 framework are accounted for the higher stability observed. The TEM investigations confirmed that the Pd nanocrystals were located within the SBA-15 mesoporous framework channels. The particle size did not exceed the mesopore diameter (2-6 nm) at Pd loading of 0.1-4.4wt.%. Pd clusters were found to be resistant against sintering during air-calcination (550 degreesC, 4h). The catalyst 2.1%Pd/SBA-15 used in methane combustion at 520 degreesC demonstrated stable activity during 6h on stream.

Structured combustion catalysts based on sintered metal fibre filters

Novel efficient structured combustion catalysts based on sintered metal fiber filters (MFF) were developed. To increase sp. surface area (SSA), metal fibers were coated by crack-free porous oxide films of SiO2, Al2O3, porous glass, and mesoporous SBA-15 silica. The composite materials presented uniform open macrostructure of the non-treated MFF filters and were suitable supports for deposition of catalytically active phases (Pd, Pt, and Co3O4). These catalysts were tested in hydrocarbon (CH4, C3H8) combustion. Co3O4 supported on MFF without any coating (6.8% Co3O4/MFF) was the most active for propane total oxidn. At the same time in methane combustion the activity of this catalyst was relatively low. Pd supported on the MFF coated by mesoporous SBA-15 film (0.5% Pd/SBA-15/MFF) demonstrated the highest activity in methane total oxidn. due to the high palladium dispersion. The SBA-15 film supported on MFF provided the highest dispersion of the deposited noble metals (Pd, Pt) with an av. particle size .apprx.2.0 nm. The metal nanoparticles formed within the mesopore channels were stable against sintering during calcination and the particle diam. was obsd. not to exceed the diam. of the silica pores. These catalysts did not undergo deactivation under reaction conditions at temps. up to 500 Deg. On the contrary, the Pd supported on MFF coated by the microporous SiO2 and Al2O3 films, prepd. by sol-gel technique, suffered from metal sintering during the calcination step and also during reaction, demonstrating strong catalyst deactivation. The catalytic filters are suitable materials for assembling different multiple layers to obtain structured catalytic beds with the compn./concn. gradients of active component in the axial direction. The enhanced overall catalytic performance was obsd. in adiabatic catalytic reactor during propane combustion due to a synergy of the 0.5% Pd/SBA-15/MFF and the 0.5% Pt/SBA-15/MFF catalytic layers assembled in the appropriate order forming gradient catalytic bed. [on SciFinder (R)]

Three-phase nitrobenzene hydrogenation over supported glass fiber catalysts: reaction kinetics study

The catalytic properties of Pd and Pt supported on woven glass fibers (GF) were investigated in the three-phase hydrogenation of nitrobenzene (NB). Over all catalysts, a 100 % yield of aniline was attained. The catalytic activity for the best catalysts was two times higher than the activity of commercial Pt/C catalyst traditionally used for liquid‐phase hydrogenation. The intrinsic reaction kinetics were studied and a reaction scheme is suggested. The direct formation of aniline from NB was observed over Pd/ GF with traces of intermediates. Four intermediate products were detected during aniline formation over Pt/GF: nitrosobenzene, phenylhydroxylamine, azoxybenzene, and azobenzene. The Eley-Rideal kinetic model fits the experimental data well. The parameters of the model were determined as a function of initial NB concentration and hydrogen pressure. Pt and Pd supported on GF in woven fabrics are suggested as suitable materials for reactors with a structured catalytic bed in multiphase reactor performance.

Cloth catalysts for water denitrification II. Removal of nitrates using Pd-Cu supported on glass fibers

The use of glass fibers in the form of woven cloth (GFC), as a new type of catalytic support, was studied for the reduction of aqueous nitrate solutions using a Pd/Cu–GFC catalyst. The activity (per gram Pd) and selectivity to nitrogen were found to be comparable with those found for Pd–Cu catalysts supported on the other carriers. The maximal initial removal activity was found for a catalyst with a Pd/(Pd+Cu) ratio of 0.81. The corresponding activity was 0.7 mmol min-1 (gPd)-1, and the selectivity was 97 mol% at 25°C and pH 6.5 for initial nitrate concentration of 100 mg l-1. The selectivity to nitrogen declined at high conversions of nitrate and high pH.

Supported glass fibers catalysts for novel multi-phase reactor design

The catalytic properties of Pd and Pt supported on woven glass fabrics were explored for liquid-phase hydrogenation of benzaldehyde as a model for three-phase catalytic reaction. The catalysts demonstrated high activity and are suitable materials to be used in reactors with structured catalytic bed. The main characteristics of catalytic bed are discussed.

Pt and Pd supported on glass fibers as effective combustion catalysts

Pd and Pt supported on glass fiber materials with developed porosity and high sp. surface areas were studied in total propane oxidn. The reaction was carried out in recycling reactor and the kinetic parameters were detd. under different reaction conditions in the temp. range 200-500 DegC. Pt catalysts were seen to be more active than Pd for the same metal loading on identical support. Catalytic activity was seen to depend on support compn. The highest activity was obsd. on Pt supported on glass fiber modified by titania, demonstrating the ignition temps. around 200 DegC. The catalyst surface morphol. and surface dispersion of active metal were characterized by high-resoln. electron microscopy. [on SciFinder (R)]

Reduction of nitrite-ions in water over Pd-supported on structured fibrous materials

The catalytic hydrogenation of nitrite in water to nitrogen over Pd-supported on different woven fibrous materials is studied. Low porosity carbon fibers, low porosity D-type glass fibers and composite (glass covered by -aluminia) fibers are used. The dispersion of Pd is compared for different supports at various Pd-loadings and correlated with the catalytic activity. The ammonia as an undesired by-product was also observed and the main parameters suppressing its formation are discussed. A reactor concept based on woven fibrous catalysts is suggested and the main design parameters for the technical application are estimated.

Metal grids with high-porous surface as structured catalysts: preparation, characterization and activity in propane total oxidation

Metal nickel and copper grids are shown to be suitable supports for structured combustion catalysts. The increase of specific surface area (SSA) of metal grids was achieved due to the porous outer layer with the structure of Raney metal developed on the wire surface. Transition metals (Co, Cu, Mn, Cr) oxides were deposited as active components on the pre-oxidized support and tested in total propane oxidation. Cobalt oxide demonstrated the highest activity. Reductive pre-treatment in the flow of hydrogen resulted in a more active catalyst than the activation in oxygen atmosphere. This effect was assigned to the partial reduction of Co3O4 until metallic Co, which was detected by XPS on the catalyst surface. Deactivation of the pre-reduced Co-oxide catalyst was observed during propane combustion in excess of oxygen and was ascribed to the oxidation of partially reduced active phase. After 4 h on stream, the catalyst reached his steady-state and showed stable activity without further deactivation. The catalytic activity expressed in the terms of propane conversion was observed to depend on the propane/oxygen ratio.

Glass fiber catalysts for total oxidation of CO and hydrocarbons in waste gases

Different glass fibers in woven forms were used as supports for Pt and Pd catalysts and were tested in toluene and CO total oxidn. at atm. pressure. The catalytic activity and the ignition-extinction temps. were investigated in relation to chem. compn. of the supports, the types of active metal used (Pt, Pd), and the surface concn. of the metal. The exptl. results suggest the modified glass fibers as suitable supports for efficient catalysts for complete oxidn. The catalysts can be used at moderate temps. (150-250 Deg) and at high gas hourly space velocity (GHSV = 30,000 h-1). The main design parameters of structured catalytic bed reactors, based on glass fiber catalyst, are discussed. [on SciFinder (R)]

Structured multiphase reactors based on fibrous catalysts: nitrite hydrogenation as a case study

A reactor concept designed as a bubble column staged with fibrous catalytic layers is tested on pilot-scale for the redn. of nitrite to N by H. CO2 is used to neutralize the hydroxide ions produced during hydrogenation of nitrite. The effective reaction rate was found to depend on the superficial gas velocity ug0. The fibrous catalysts demonstrated a high selectivity towards nitrogen. The influence of the mass transport on the effective kinetics is discussed and the volumetric liq.-solid mass transfer coeff. kSaS is estd. as a function of the superficial gas velocity ug0. The selectivity was found to be independent of the hydrodynamics.