V.S. Kamble

Gold promoted S,N-doped TiO(2): an efficient catalyst for CO adsorption and oxidation.

Mesoporous S,N-TiO(2) nanocomposite was prepared by a one-pot template free homogeneous coprecipitation technique using titanium oxysulfate sulfuric acid complex hydrate, thiourea, ethanol, and water. Nano gold deposition on mesoporous S,N-TiO(2) was preformed by a borohydrate reduction method. To evaluate the structural and electronic properties, these catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), UV-vis DRS, photoluminescent (PL) spectra, Fourier transform infrared (FTIR), and TPO/TPD. CO adsorption and CO + O(2) interaction over these catalysts were investigated by in situ FTIR. Sulfur and nitrogen doping enhances the catalytic activity of Au/TiO(2.) Higher catalytic activity of Au/S,N-TiO(2) compared to Au/TiO(2) was attributed to the presence of oxygen vacancy and creation of new adsorption sites at Au/TiO(2) interfaces for the adsorption and activation of O(2) molecules.

FTIR spectroscopic study of the interaction of CO2 and CO2 + H2 over partially oxidized Ru/TiO2 catalyst

At least three distinct linearly bound carbonyl species are identified in the adsorption of CO2 or CO2 + H2 over RuRuOxTiO2 catalyst. The relative concentration and the growth of these species depend on metal oxidation state, presence of hydrogen, reaction temperature, and duration of exposure. The presence of preadsorbed or coadsorbed hydrogen promotes formation of x173-1 type species, the RuOx-(CO)ad species develop only on prolonged exposure to a dose of CO2 or CO2 + H2. The oxygen or the hydrogen ligand bonded to ruthenium facilitates CO bond scission. The widely reported lower temperature requirement for the CO2 methanation reaction as compared to that of CO is attributed to the high reactivity of nascent carbonyl species which give methane directly via “active” carbon formation. As shown earlier (Gupta et al., J. Catal. 137, 437 (1992)), the CO methanation requires multistep transformations, making the process energy intensive, particularly in the 300–450 K temperature range. The studies using 2H and 13C labeled adsorbates helped in the identification of oxygenated surface species having vibrational bands in the 1000–1800 cm−1 region. These species are regarded as inactive side products formed on the support and/or at the Ru-support interfaces.

Friedel-Crafts benzoylation of p-xylene over clay supported catalysts: novelty of cesium substituted dodecatungstophosphoric acid on K-10 clay

Abstract 2,5-Dimethylbenzophenone is used extensively as a UV light stabilizer in plastics, cosmetics and films and produced by the benzoylation of p -xylene using homogeneous catalysts which pose several problems. The benzoylation of p -xylene with benzoyl chloride was carried out in a batch reactor using clay supported catalysts such as 20% (w/w) dodecatungstophosphoric (DTP) acid/K-10, 20% (w/w) Cs 2.5 H 0.5 PW 12 O 40 /K-10, 20% (w/w) ZnCl 2 /K-10 and K-10 itself and sulfated zirconia. Amongst these catalysts, 20% (w/w) Cs 2.5 H 0.5 PW 12 O 40 /K-10 was found to be a better catalyst which could be reused without any further chemical treatment eliminating the effluent disposal problem. This catalyst was fully characterized. The reaction obeys the Eley–Rideal type of mechanism with a weak adsorption of the benzoylating species.

The Role of Nanosize Particles of Uranium Oxide in the Adsorption/Reaction of Methanol Over U3O8/MCM-48: FTIR Study

The surface species formed over MCM-48, U3O8 and U3O8/ MCM48 catalysts during the adsorption/reaction of methanol were monitored using FTIR spectroscopy, in order to get an insight into the high catalytic activity exhibited by the nanosize crystallites of uranium oxide dispersed in MCM-48. The results of this in situ study revealed that the title catalysts exhibited a distinct behavior for adsorption and subsequent reaction of methanol. Thus, while the room temperature adsorption over bulk U3O8 resulted in the formation of formate complex and oxymethylene species, the interaction over MCM-48 resulted in simultaneous and instant formation of surface methoxy groups and dimethyl ether. On the other hand, the exposure of methanol over U3O8/MCM-48 under similar conditions resulted in the appearance of intense IR bands due to surface-adsorbed (–OCH2)n species, where n≥1, in addition to those of formate complexes, oxymethylene and methoxy groups. The role of the above-mentioned intermediate species in the formation of different reaction products is discussed in brief.

Effect of hydrogen reduction on the CO adsorption and methanation reaction over Ru/TiO2 and Ru/Al2O3 catalysts

The C–O stretch vibrational bands developed over Ru/TiO2 and Ru/Al2O3 catalyst surfaces during adsorption of CO at different temperatures were investigated as a function of H2 pretreatment given to a sample in the temperature range of 575–875 K. While the reduction at temperatures below 675 K had no significant effect, the higher temperature H2 pretreatment resulted in the progressive annihilation of νCO bands in the 2050–2145 cm−1 region, identified with the multicarbonyl species bonded to Ru sites of different oxidation states. The removal of these bands showed a parallelism with the loss of catalyst activity at reaction temperatures below 500 K, whereas the activity at the temperatures above 550 K remained almost unaffected. We conclude that the Ru(CO)n species are formed over highly dispersed metal surfaces and are responsible to the low temperature catalytic activity. On the other hand, the catalytic activity at higher reaction temperatures is attributed to certain monocarbonyl moieties, the formation of which is rather independent of metal dispersion. Our results also reveal the occurrence of the reductive surface agglomeration of Ru metal at high temperatures and the reformation of the smaller crystallites on subsequent exposure of the catalyst to O2.

Effect of. gamma. -irradiation on methanation of carbon dioxide over supported Ru catalysts

In situ γ-irradiation has been found to enhance the activity of Ru/molecular sieve and Ru/alumina catalysts for the CO2 methanation reaction in the temperature range 400–600 K. The extent of radiation enhancement in catalytic activity was inversely related to temperature. The activation energy for the formation of CH4 from 2% CO2 in H2 was reduced in the presence of radiation from 13.8 to 7.7 kcal mole−1 for Ru/alumina and from 7.3 to 4.2 kcal mole−1 for Ru/molecular sieve. The results indicate that γ-irradiation gives rise to energy storage in support materials. It is suggested that the energy released on thermal stimulation weakens the metal-CO2 bonds resulting in an accelerated rate of reduction of CO2 to active carbon and its subsequent methanation.

Co adsorption-desorption properties of cation-exchanged NaX zeolite and supported ruthenium

The binding states of carbon monoxide over cation-exchanged NaX zeolites and over corresponding Ru-containing samples have been investigated using thermal desorption spectroscopy. Exchange of sodium with cations such as Li+, Ca2+, Mg2+, and La3+ gave rise to additional CO adsorption states, a higher isosteric heat of CO adsorption, an increased density of acid sites, and an increased amount of adsorbed CO, depending on the nature and ionic radius of the chargebalancing cation. The charge-balancing cations at the zeolite surface (e.g., Ca2+, La3+) function as additional CO adsorption sites in conjunction with surface acid centers (e.g., the A13+ center) and metal sites. In addition to surface sites, CO is also found to be held in structural cavities and macropores of the zeolite matrix. The programmed heating of both the metal-free and Ru-containing zeolites subsequent to room temperature CO adsorption gave desorption peaks due to release of CO at temperatures less than ~500 K while the higher temperature peaks were constituted mainly of CO2. Electron spectroscopy results have revealed that the exposure of these samples to CO and subsequent thermal treatment resulted in the formation of surface carbonaceous species. The nature of CO adsorption states giving rise to CO2 formation is discussed.

Effect of γ-irradiation on methanation of carbon monoxide over Ru/molecular sieve catalyst

Abstract The effect of in situ γ-irradiation on methanation of carbon monoxide has been studied at different temperature in the range 400–575 K using a molecular sieve supported Ru catalyst. At temperatures less than 500 K, irradiation has been found to result in a large increase in catalytic activity. The enhancement in methane yields was dependent on the temperature of the catalyst, CO/H2 ratio and γ-dose. Thermoluminescence studies have shown that on γ-irradiation, energy is stored in molecular sieves in the form of trapped centres which get released on thermal stimulation. Enhanced catalytic activity has been attributed to the transfer of energy from the molecular sieve support to ruthenium which leads to an accelerated rate of reaction of H2 with active carbon and CO2, which are produced in the disproportionation reaction of carbon monoxide on the catalyst surface.

FTIR studies on the CO, CO2 and H2 co-adsorption over Ru-RuO x /TiO2 catalyst

FTIR spectra of a Ru-RuOx/TiO2 catalyst obtained on co-adsorption of CO, CO2 and H2 in the temperature range of 300–500 K were found to be the sum total of corresponding spectra observed during methanation of individual oxides. The two oxides compete for metal sites and at each temperature they reacted simultaneously to form distinct transient Ru(CO)n type species even though the nature, the stability and the reactivity of these species were different in the two cases. The monocarbonyl species formed during adsorption/reaction of CO alone or of CO + H2 were bonded more strongly than those formed during CO2 + H2 reaction.

Carbon monoxide adsorption/desorption processes over NaX zeolite and supported ruthenium catalyst

The binding states of CO on NaX zeolite and RuNaX were investigated by thermal desorption spectroscopy. Desorption peaks centred at around 390, 430, 490, and 520 K were observed from NaX following room-temperature adsorption of CO. The activation energy values corresponding to these peaks were calculated to be 41.4, 45.7, 53.8, and 57.7 kJ mol−1, respectively. These peaks were also observed in desorption profiles from RuNaX although their temperatures were higher by 10 to 20 K. In addition, the desorption spectra from RuNaX also comprised two high-temperature peaks at around 575 and 640 K. With both the RuNaX and the NaX samples, the temperature and relative intensities of the desorption peaks depended on pretreatment conditions and on the lapsed time between CO exposure to the sample and the commencement of programmed heating. Mass spectral analysis revealed that the gas desorbed at 300–500 K consisted mainly of CO while at higher temperatures CO2 was the main component. The desorption peaks below 500 K are attributed to the release of carbon monoxide from structural and intragranular or intergranular zeolitic pores. Lewis sites on the zeolite surface are found to facilitate activation of CO, resulting in its transformation to CO2. The initial adsorption of carbon monoxide in zeolite pores and subsequent diffusion to metal sites leading to its disproportionation/oxidation is found to play an important role in the CO adsorption/desorption process on RuNaX.