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)

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 liq.-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. [on SciFinder (R)

Benzene Hydroxylation over FeZSM-5 Catalysts: Which Fe-sites Are Active?

FeZSM-5 with a wide range of Fe content (0.015–2.1 wt%) were studied in the benzene hydroxylation to phenol with nitrous oxide (C6H6:N2O = 1:5) at low temperatures (98%) was obtained within 3 h without any deactivation of the catalyst. Three types of Fe(II) sites were formed in the zeolites extraframework due to activation and are attributed to: (1) Fe(II) sites in mononuclear species, (2) oligonuclear species with at least two oxygen-bridged Fe(II) sites, and (3) Fe(II) sites within Fe2O3 nanoparticles. The degree of nuclearity of Fe(II) species was observed to increase with iron content and activation temperature/time. The total amount of Fe(II) sites was monitored by the transient response method of the N2O decomposition (523 K) accompanied by the formation of surface atomic oxygen (O)Fe. Only mono- and oligonuclear Fe(II) sites active in CO oxidation seem also to be responsible for the FeZSM-5 activity in benzene hydroxylation. Their amount was measured by the transient response of CO2 during CO oxidation on zeolites preloaded by (O)Fe. The turnover frequencies in the benzene oxidation were constant independently of the catalyst activation in the isomorphously substituted zeolites. The Fe(II) ions in nanoparticles (inactive in hydroxylation) are probably irreversibly reoxidized by N2O to Fe(III), which are known to be responsible for the total oxidation of benzene

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 sp. 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 oxidn. 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 atm. This effect was assigned to the partial redn. of Co3O4 until metallic Co, which was detected by XPS on the catalyst surface. Deactivation of the pre-reduced Co-oxide catalyst was obsd. during propane combustion in excess of oxygen and was ascribed to the oxidn. 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 obsd. to depend on the propane/oxygen ratio. [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

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)

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

Catalytic hydrogenation of NO2- in water to N2 over Pd-supported on different woven fibrous materials was studied. Low porosity C fiber, low porosity D-type glass fiber, and composite (glass covered by g-Al2O3) fiber were used. Pd dispersion was compared for different supports at various Pd loadings and correlated with catalytic activity. NH3 as an undesired byproduct was also obsd. and main parameters to suppress its formation are discussed. A reactor concept based on woven fibrous catalysts is suggested and main design parameters for tech. application were estd. [on SciFinder (R)

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)

Highly dispersed gold on activated carbon fibers for low temperature CO oxidation

Gold nanoparticles of 2–5 nm supported on woven fabrics of activated carbon fibers (ACF) were effective during CO oxidation at room temperature. To obtain a high metal dispersion, Au was deposited on ACF from aqueous solution of ethylenediamine complex [Au(en)2]Cl3 via ion exchange with protons of surface functional groups. The temperature-programmed decomposition method showed the presence of two main types of functional groups on the ACF surface: the first type was associated with carboxylic groups easily decomposing to CO2 and the second one corresponded to more stable phenolic groups decomposing to CO. The concentration and the nature of surface functional groups was controlled using HNO3 pretreatment followed by either calcination in He (300–1273 K) or by iron oxide deposition. The phenolic groups are able to attach Au3+ ions, leading to the formation of small Au nanoparticles (9 nm) Au agglomerates after reduction by H2. These catalysts demonstrated lower activity as compared to the ones containing mostly small Au nanoparticles. Complete removal of surface functional groups rendered an inert support that would not interact with the Au precursor. The oxidation state of gold in the Au/ACF catalysts was controlled by X-ray photoelectron spectroscopy before and after the reduction in H2. The high-temperature reduction in H2 (673–773 K) was necessary to activate the catalyst, indicating that metallic gold nanoparticles are active during catalytic CO oxidation