J.I. Gutiérrez-Ortiz

Enhanced activity of zeolites by chemical dealumination for chlorinated VOC abatement

Abstract The objective of this work is to evaluate the dealumination via ammonium hexafluorosilicate treatment as an effective method for enhancing the catalytic performance of H-Y zeolite in chlorinated VOC oxidative destruction. A series of Y zeolites with various Si/Al ratios was prepared from a commercial sample and then tested for the catalytic decomposition of 1,2-dichloroethane as a model reaction. In general, these modified Y zeolites exhibited a higher activity than that of the parent material, the zeolite subjected to 50% dealumination resulting the most active catalyst. This increase in activity was associated with the development of strong acidity due to dealumination. Likewise, 50% dealuminated sample showed an improved catalytic behaviour for the destruction of other typical chlorinated pollutants, namely, dichloromethane (DCM) and trichloroethylene (TCE). The ease of destruction was found to follow this trend: 1,2-dichloroethane > dichloromethane > trichloroethylene.

Nickel on silica systems. Surface features and their relationship with support, preparation procedure and nickel content

Abstract The characteristics and structure of several silica-supported nickel systems, prepared by impregnation and precipitation-deposition and in a wide range of nickel contents (from 0.58 up to 69 wt% Ni), have been studied. Using mainly conventional sorption techniques the textural properties - BET surface area, pore volume, average pore radius, pore size distribution - and surface chemical distribution - nickel surface area, reduction degree, dispersion, crystallite particle diameter - of the samples have been determined. All these characteristics have been related to each other and globally analyzed to advance in the understanding of the final structure of the catalysts and its relationship with support structure, preparation procedure and nickel content.

Effect of thermal treatments on surface chemical distribution and catalyst activity in nickel on silica systems

The reducibility of several nickel on silica systems prepared by incipient wetness impregnation and precipitation-deposition has been studied using TPR and TG. The analysis of the results has allowed us to determine the minimum drying and reduction temperatures for both impregnation and precipitation catalysts. From an analysis of the obtained results, together with X-ray diffraction and the study of the reduction degree, dispersion and nickel particle size of catalysts activated at different reduction temperatures, conclusions on the nickel surface chemical distribution have been derived. An optimal reduction temperature for the catalysts has been determined from activity considerations in the hydrogenation of sunflower seed oil.

Catalytic behaviour of H-type zeolites in the decomposition of chlorinated VOCs

Abstract Several H-type zeolites were investigated for their activity and selectivity during TCE oxidative decomposition in dry and humid conditions. These catalysts showed high activity resulting H-MOR to be the most active. The catalytic behaviour appeared to be determined by strong Bronsted acidity. The main oxidation products were CO, CO 2 , HCl and Cl 2 . Water enhanced the catalytic activity at lower temperatures and also promoted the selectivity to deep oxidation products generation (CO 2 and HCl).

Effect of Pd addition on the catalytic performance of H-ZSM-5 zeolite in chlorinated VOCs combustion

The aim of this work was to evaluate the influence of the addition of palladium on the catalytic behaviour of H-ZSM-5 zeolite in the combustion of 1,2-dichloroethane (DCE) and trichloroethylene (TCE). Both catalysts showed similar activity in the oxidation of DCE, by contrast, the metal loading led to a substantial improvement in TCE combustion. Vinyl chloride was detected as an intermediate in DCE conversion, and it was appreciably suppressed when adding Pd to the zeolite. In TCE oxidation trace amounts of tetrachloethylene were identified as a by-product, Pd/H-ZSM-5 showing larger quantities of this undesired by-product. Pd/H-ZSM-5 was more selective towards CO2 formation instead of CO, which was the major carbon-containing product formed over H-ZSM-5. However, H-ZSM-5 zeolite showed a lower selectivity to Cl2 generation while the metal loaded zeolite considerably promoted the formation of this toxic by-product by the Deacon reaction.

Prediction of lifetime of poly(2-hexyne) films through the kinetics of thermooxidative degradation from thermogravimetric and molecular weight data

Substituted polyacetylenes suffer from important degradation in contact with air at moderately high temperatures, making them useless since some mechanical properties are lost. To predict the lifetime a kinetic study of the thermooxidative degradation process for poly(2-hexyne) is presented. Thermogravimetry and GPC have been used to analyse some variables representative of polymer degradation, namely weight loss due to emission of volatiles, oxygen uptake and molecular weight evolution. The weight of the samples presented an initial increase (due to oxidation) followed by a quasi-linear decrease (due to volatilization). A mechanism considering both phenomena has been proposed and modelled, resulting in a kinetic equation which satisfies the whole degradation process. The evolution of weight loss has also been related to the chain scission, obtaining a linear dependence in agreement with the proposed degradation kinetic model. However, accurate quantification of oxygen uptake presented some problems so that this variable can only be considered as a qualitative indication of the degradation level.

Catalytic Performance Of Chlorinated Ce/ZrMixed Oxides For Cl-VOC Oxidation

Contamination by chlorinated volatile organic compounds (Cl-VOCs) is currently a matter of considerable concern, since these compounds are considered as dangerous for their effect on human health and the environment. Catalytic oxidation appears as an attractive approach for the destruction of these hazardous compounds. Although the development of catalysts to produce CO2 and HCl is a topic of demanding interest, less consideration has been given to examining the catalytic stability during extended time on stream. Indeed the presence of HCl and/or Cl2 may induce alterations in the behaviour of the catalysts. The main scope of this work is to evaluate the catalytic behaviour of a series of Ce/Zr mixed oxides in the gas-phase oxidation of 1,2-dichloroethane submitted to a previous chlorination followed by calcination (550 oC for 4 hours in air) or by reduction (550 oC with 5%H2/Ar for 1 hour) and calcination. Chlorination led to remarkable changes in acidity and redox properties, which were shown to be the key catalytic properties of these catalysts for this reaction. On one hand, the chlorine reinforced the acidity of the catalytic surface. In contrast, redox properties were negatively impacted. However, these alterations were partially compensated leading to a slightly lower activity of chlorinated samples. It could therefore be concluded that Ce/Zr catalysts resulted in significant resistance to deactivation by chlorine poisoning, thereby showing a great potential for this environmental application, not only in terms of lowtemperature Cl-VOC conversion, but also of stability during extended periods of time on stream.

81 Gas-phase catalytic decomposition of mixtures of low-molecular-weight chlorinated VOCs

Abstract The oxidative decomposition of binary mixtures of chlorinated VOCs (1.2-dichloroethane, dichloromethane and trichloroethylene) over H-ZSM-5 and chemically dealuminated H-Y zeolite catalysts has been investigated. The ease of destruction decreased in the order: DCE>DCM>TCE. The main oxidation products were CO, CO 2 , HCl and Cl 2 . Some other chlorinated by-products were detected as well (vinyl chloride, methyl chloride and tetrachloroethylene). The destruction of binary mixtures induced an inhibition of the oxidation of each chlorinated compound. Likewise, an important decrease in the formation of intermediates was noticed, and HCl selectivity was largely improved.

Mass Transfer Studies in the Hydrogenation of Methyl Oleate Over a Ni/SiO2 Catalyst in the Liquid Phase

A detailed mass transfer analysis was developed both theoretically and experimentally for the heterogeneously catalyzed hydrogenation of methyl oleate using a Ni/silica catalyst in a slurry reactor. The results indicate that, at the conditions studied, working with stirring rate between 1400 and 2000 rpm, catalyst particle size below 50 µm, and catalyst weight below 1.11 g assured the kinetic regime for the reaction.

Chemical Recycling Of PET By AlkalineHydrolysis In The Presence Of QuaternaryPhosphonium And Ammonium Salts As PhaseTransfer Catalysts

Chemical or tertiary recycling of waste polymers including PET, poly(ethylene terephthalate), is the only method according to the principles of Sustainable Development, since it leads to the formation of the raw materials (monomers) from which the polymer is made of. This work has been focused on the determination of the kinetics of the depolymerisation of PET by means of alkaline hydrolysis and on the identification of the catalytic behaviour, if any, of a series of phosphonium and ammonium salts as phase transfer catalysts (9 salts with varying alkyl groups, central cation (N or P) and anion (Cl, Br, I, OH)). Among the catalysts tested tributylhexadecylphosphonium bromide (3Bu6DPB) is found to be the most effective catalyst. Complete conversion of PET with considerably low catalyst concentration and temperature can be achieved. The selected phase transfer catalyst fulfils the requirements of having enough character in order to be lipophilic, while small enough in order to avoid steric hindrance. The time for complete hydrolysis (>90% conversion) of solid PET under alkaline conditions with 3Bu6DPB at 80 oC is 1.5 hours and 10 hours without 3Bu6DPB.