José A. González-Marcos

Pervaporation of ethanol—water mixtures through poly(1-trimethylsilyl-1-propyne) (PTMSP) membranes☆

The separation of alcohol—water mixtures by pervaporation has been preferentially carried out through hydrophobic membranes because it is more practical to permeate alcohol through the membrane. Nevertheless, most polymeric membranes are water permselective as the molecular size of water is smaller than that of ethanol. Ethanol-permselective membranes have been limited to silicon- and fluorine-containing polymers, for example, polydimethylsiloxane (PDMS), poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(tetrafluoroethylene) derivatives. PTMSP is known to show preferential permeation of ethanol in the pervaporation of ethanol—water mixtures. The permselectivity of this material is related to the existence of free volume and to the hydrophobicity of the membrane surface. The separation factor (αH2OEtOH) reached a value of 10.7 at 10 wt% of ethanol in the feed, and after 450 h it decreased to an average value of 8. The initial value is similar to that of PDMS, a well-known etanol-permselective membrane. Although PTMSP presented good characteristics for the separation of ethanol—water mixtures, the separation factor and the specific permeation rate (R) decrease with operation time due to a swelling process; however, the latter reached a value similar to the initial one after this period.

Influence of water and hydrocarbon processed in feedstream on the three-way behaviour of platinum-alumina catalysts

Abstract The influence of water and the nature of the hydrocarbon -methane, ethylene, propene and 1-butene- processed in the feedstream on the three-way behaviour of a ceria-modified alumina supported platinum catalyst is investigated. Experiments were carried out with static feedstreams with air-to-fuel ratios between 14.13 and 15.17 as well as with oxidizing-reducing cycled feedstreams simulating the real automobile exhaust mixture. Conclusions are drawn on the importance of water-gas shift and steam reforming reactions and their relationship with inhibition self-poisoning effects of carbon monoxide and/or hydrocarbons. Comparison of data of the prepared catalyst and those obtained at the same operational conditions with two commercial catalysts, with only platinum/alumina and platinum-rhodium/ceria-alumina respectively, allows confirmation of the effects of ceria and establishes the role of rhodium when added to the catalyst.

Kinetic considerations of three-way catalysis in automobile exhaust converters

Abstract The activity of three-way catalysts is highly dependent on the reactants present in the automobile exhaust gases (CO, NO x , HC, O 2 , H 2 O, CO 2 , N 2 ) as well as their relative concentration. Thus, the influence of each reactant on the kinetic behavior of the whole mixture makes difficult to establish the accurate kinetics of the system. Activity experiments carried out close to the real operation conditions (GHSV, concentration, etc.) with a Pt/CeO 2 /Al 2 O 3 catalyst supplied data on the CO and HC oxidation and NO reduction reactions in environments formed by different reactant combinations (from binary mixtures to the whole mixture simulating the real conditions at the automobile converter). The obtained results have shown notable variations in the oxidation/reduction mechanisms depending on the presence (or absence) of components in the environment. The presence of water always promoted the three-way activity of the catalyst. The compensation effect applied to the CO, NO and HC conversions confirmed that kinetic expressions obtained with partial mixtures (not very close to the real converter environment) have only limited application for determining the whole kinetic scheme occurring in the automobile converters.

State of the art in catalytic oxidation of chlorinated volatile organic compounds

Chlorine-containing organic compounds (Cl-VOC) require special attention due to their distinct toxicity, high stability and persistence in the environment. Removal of Cl-VOC by catalytic oxidation over a wide variety of catalysts has been presented in literature. This paper reviews the state of the art in this subject, including different model compounds, nature of catalysts, and oxidation activity. Catalyst selectivity (CO2 vs. CO and HCl vs. Cl2), by-products formation and the causes of deactivation are also analyzed as the most important factors in the catalyst selection for practical applications.

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.

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.

Lithium Bis(fluorosulfonyl)imide/Poly(ethylene oxide) Polymer Electrolyte for All Solid-State Li–S Cell

Solid polymer electrolytes (SPEs) comprising lithium bis(fluorosulfonyl)imide (Li[N(SO2F)2], LiFSI) and poly(ethylene oxide) (PEO) have been studied as electrolyte material and binder for the Li-S polymer cell. The LiFSI-based Li-S all solid polymer cell can deliver high specific discharge capacity of 800 mAh gsulfur-1 (i.e., 320 mAh gcathode-1), high areal capacity of 0.5 mAh cm-2, and relatively good rate capability. The cycling performances of Li-S polymer cell with LiFSI are significantly improved compared with those with conventional LiTFSI (Li[N(SO2CF3)2]) salt in the polymer membrane due to the improved stability of the Li anode/electrolyte interphases formed in the LiFSI-based SPEs. These results suggest that the LiFSI-based SPEs are attractive electrolyte materials for solid-state Li-S batteries.

Optimal inlet temperature trajectories for adiabatic packed reactors with catalyst decay

Abstract An algorithm for simulation and optimization of adiabatic fixed-bed reactors subject to catalyst deactivation is developed. It is applied to the low-temperature CO converter, the kinetic model for which is deduced from some industrial data and considering chlorine as the main cause of catalyst poisoning. Sintering is not considered due to the short range of variation of temperature in the catalyst bed. Optimal inlet temperature trajectories are determined to maximize the obtained total amount of reaction over a fixed operation time. Approximate optimal trajectories in discrete steps of temperature are proposed to be followed in industrial practice.

Screening of Fe–Cu-Zeolites Prepared by Different Methodology for Application in NSR–SCR Combined DeNOx Systems

The NOx NH3-SCR performance of several Cu and Fe catalysts supported on BETA and ZSM-5 zeolites has been studied in single SCR and double NSR–SCR configuration, and the activity related to the nature and reducibility of metal species on the catalyst surface. Intermediate ammonia formed in NSR improved greatly NOx conversion at the exit of the double NSR–SCR configuration, which was practically totally converted to N2.

Deep catalytic oxidation of chlorinated VOC mixtures from groundwater stripping emissions

The total oxidation chlorinated VOCs mixtures, with composition similar to those expected from groundwater air strippers, over Pd/Al2O3 and Pt/A2O3 catalyst at temperatures from 200 to 550°C was investigated. 1,2-Dichloroethane showed greater oxidability, followed by dichloromethane and 1,1- dichioroethylene and trichloroethylene. The addition of hydrocarbons to a chlorinated feed produced changes in the reactivity order of the chlorinated VOCs, indicating the existence of a complex reaction system due to the energetically non-uniform catalytic surface.