José I. Gutiérrez-Ortiz

Gas-phase catalytic combustion of chlorinated VOC binary mixtures

Abstract The complete oxidation of 1,2-dichloroethane (DCE), dichloromethane (DCM) and trichloroethylene (TCE) as individual chlorohydrocarbons and of their binary mixtures over protonic zeolites (H-ZSM-5, H-MOR and chemically dealuminated H-Y zeolite) has been studied using a conventional fixed bed flow reactor. Its catalytic performance was associated with the presence of strong Bronsted acidity. Both H-MOR and chemically dealuminated H-Y zeolites exhibited the highest destruction activity for the abatement of single and binary mixtures. The destruction of chlorinated mixtures induced an inhibition of the reactivity of each compound leading to a significant increase in the ignition temperature, which varied form one compound to other. On the other hand, a moderate decrease in chlorinated intermediates/by-products formation was noted. Likewise, the presence of hydrogen, either as a part of the additional chlorinated molecule or as a part of water generated as a reaction product, was determined to be important for efficient combustion of the chlororganics to HCl.

Preparation, activity and durability of promoted platinum catalysts for automotive exhaust control

Abstract The effects of the addition of calcia, ceria and lanthana to alumina-supported platinum catalysts on the simultaneous control of hydrocarbon, carbon monoxide and nitrogen oxide automobile emissions (three-way catalyst behaviour) were analyzed. The activity of the prepared samples was determined with steady-state, reducing and oxidizing, simulated feedstreams as well as with a cycled oxidizing-reducing feedstream averaged at the stoichiometric conditions which resembled the exhaust air/fuel fluctuations in a closed-loop emission control system. Activity of the catalysts was also analyzed after conducting accelerated thermal and chemical ageing in order to test their durability. Under normal operating conditions of the automobile engine, Pt/Al2O3 catalysts promoted by rare-earth oxides are able to achieve high HC, CO and NO conversions. The behaviour of the catalysts in the cold start period was determined by analysis of light-off temperatures and a comparison was made with those corresponding to some commercial samples and others reported in the literature. The catalysts prepared in this work showed lower light-off temperatures than those of commercial and reported Pt/Al2O3 catalysts but these temperatures were not so low as with PtRh/Al2O3. In all cases, the prepared catalysts resulted in a better resistance to accelerated ageing. Samples with ceria showed the best resistance to accelerated ageing.

Role of water and other H-rich additives in the catalytic combustion of 1,2-dichloroethane and trichloroethylene.

In several practical applications gas streams containing chlorinated volatile organic compounds with variable chemical nature (namely, 1,2-dichloroethane and trichloroethylene) and a significant moisture content (15000ppm) must be addressed. In this paper the control of such emissions by catalytic oxidation over Ce/Zr mixed oxides was analysed. Results in terms of activity and selectivity were compared with those obtained when other H-rich additives (1000ppm), such as hexane or toluene, were fed. High activity was found from mixed oxides featuring a suitable combination of a large population of acid sites, easily accessible oxygen species, and hydrophobic nature attributable to cerium content. The presence of additional H-rich compounds in the feed stream (water, toluene or hexane) tended to decrease the catalytic activity due to the blockage and/or competition for actives sites. However, the increased presence of hydrogen atoms in the stream notably promoted the selectivity to hydrogen chloride instead of molecular chlorine.

Kinetics of the selective hydrogenation of phenol to cyclohexanone over a Pd-alumina catalyst

The most suitable kinetic equation for the selective hydrogenation of phenol to cyclohexanone on a 0.96wt.% Pd-9.63wt.%CaO-alumina (Harshaw AL-3965) catalyst is determined among a series of models based on Langmuir-Hinshelwood-Hougen-Watson theory.AbstractОпределено кинетическое уравнение селективного гидрирования фенола до циклогексанона на катализаторе 0,96 вес. %Pd-9,63 вес.%CaO/Al2O3 (Harshaw AL-3965). Оно оказалось наиболее подходящим среди серии моделей, основанных на теории Лангмюра-Хинщельвуда-Хугена-Ватсона.

Oxidation of chlorinated alkanes over Co3O4/SBA-15 catalysts. Structural characterization and reaction mechanism

Cobalt oxide-based catalysts have been synthesised via a hard template of mesoporous silica SBA-15 in the form of massive Co3O4 nanoparticles, whose dimensions are controlled and limited by the support mesoporosity. Over this family of catalysts, both weak Bronsted and Lewis acidities have been detected, with the relative abundance a function of the cobalt content. The mesoporosity of the support leads to the growth of oxide nanoparticles, mainly in the small pores, thus improving their redox properties. Catalysts possessing cobalt oxide loadings higher than 30% present an adequate activity for the deep DCE oxidation toward carbon dioxide, hydrogen chloride and chlorine. It is believed that the reaction is markedly accelerated due to the simultaneous participation of the acid sites (where the chlorinated feed is efficiently adsorbed) and the redox sites (oxidation of the adsorbed feed with lattice oxygen anions). FTIR data on dichloroalkane oxidation evidence that lattice oxygen species are mainly involved in the Cl-VOC combustion, likely through a Mars–van Krevelen mechanism.

The control of the temperature and the feed in deactivating isothermal catalyst beds

Abstract A comparison of the space time policy and the temperature policy to be followed in order to maintain a constant outlet conversion in spite of catalyst Graphic design charts which allow the catalyst lifetime and the production for a given conversion rate to be determined are presented for both strategi Finally, catalyst lifetime and production values obtained following these policies are compared.

Inverse gas chromatography as a technique for the characterization of the performance of Mn/Zr mixed oxides as combustion catalysts

Adsorption of different volatile organic compounds (trichloroethylene, TCE; 1,2-dichloroethane, DCE; n-hexane) over different manganese-zirconia mixed oxides (Mn(x)Zr(1-x)O(2)) - widely used as combustion catalysts - was studied by inverse gas chromatography. Adsorption isotherms (calculated in the Henry region), adsorption enthalpies (DeltaH(ads)), and dispersive (gamma(S)(D)) and specific (I(sp)) components of the surface energy have been determined at infinite dilution for the investigated compounds. Both the adsorption enthalpy and the specificity of the interaction of TCE and DCE over Mn(x)Zr(1-x)O(2) catalysts depend strongly on manganese content. Thus, the adsorption strength of the reactants over the active sites is closely related with both the surface acidity and the accessibility of the lattice oxygen. A great influence of the specific interaction on the catalytic pattern has been also noticed. Since I(sp) depends on the redox properties, it has been proved that the specific interaction is determined by the presence of bulk Mn(3)O(4), which hinders the mobility of the oxygen lattice, and MnO(x), with the contrary effect. Finally, the selectivity to oxidation products has been correlated with both the enthalpy of adsorption and the specific interaction parameter, decreasing the selectivity to HCl with the increase of the enthalpy of adsorption.

Analysis of the Behaviour of Different Mixed Oxides in the Treatment of Cl-VOC Containing Gas Streams

The present work deals with the catalytic behaviour of a series of ceria and manganese-based catalysts for the deep single combustion chlorinated compounds in air. Our attention is focused on both activity and product selectivity of Ce/Zr and Mn/Zr in the oxidation of 1,2-dichloroethane (1,000 ppm) and trichloroethylene (1,000 ppm). This study also makes an attempt to establish a correlation between physico-chemical properties and catalytic performance.Both series of mixed oxides exhibited a noticeable activity in the combustion of both compounds, Ce0.5Zr0.85O2, Ce0.5Zr0.5O2 and Mn0.4Zr0.6O2 being the samples with the most promising catalysts. A remarkable acidity and readily accessible active oxygen species played a key role in determining the catalytic behaviour. As for the product selectivity, CO2, CO, HCl and Cl2 were the main products. The yield of CO2 and Cl2 was favoured as cerium or manganese content was increased. However, selectivity to chlorine was noticeably limited by the addition of stream in favour of HCl.

Surface activity of silice-alumina catalysts in relation to the preparation variables

Factorial and rotational designs have been used to analyse the effect of each preparative variable on the surface acid strength distribution in silica-alumina catalysts. Relationships between the surface acidities at pKa = 2·8, 3·3 and 4·8 and the most important variables, namely precipitation rate and temperature, drying pressure and temperature, impregnation concentration and calcination temperature have been obtained.

Promoter Effects on Platinum Catalysts for Automotive Exhaust Control

Abstract The promoter effect of calcium, cerium and lanthanum oxides on the physical, chemical, and catalytic properties of alumina-supported platinum catalysts for the automotive exhaust control has been analysed. The prepared catalysts have been tested at net oxidizing, net reducing and stoichiometric conditions. The catalytic behaviour has also been analysed after thermal and/or chemical accelerated aging.