Person:
Martín Martínez, María

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First Name
María
Last Name
Martín Martínez
URI
https://hdl.handle.net/20.500.14352/76250
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Ingeniería Química y de Materiales
Area
Ingeniería Química
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2010 - 20133
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Author: Gómez-Sainero, L.M. × Start date: 2010 ×

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Now showing 1 - 3 of 3
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    Comparison of different precious metals in activated carbon-supported catalysts for the gas-phase hydrodechlorination of chloromethanes
    (Applied Catalysis B: Environmental, 2013) Martín Martínez, María; Gómez-Sainero, L.M.; Alvarez-Montero, M.A.; Bedia, J.; Rodriguez, J.J.
    Four precious metals supported on activated carbon are compared as catalysts in the gas-phase hydrodechlorination (HDC) of chloromethanes. The intrinsic activity or turnover frequency (TOF) of the catalysts follows the order Pd/C > Rh/C > Pt/C > Ru/C in the HDC of dichloromethane (DCM) while the sequence Pd/C > Pt/C > Rh/C > Ru/C was found for the HDC of chloroform (TCM). High selectivities to non-chlorinated products were obtained in all cases except for the HDC of TCM with Rh/C and Ru/C where the selectivity to DCM greatly depends on the operating conditions. A wider diversity of non-chlorinated hydrocarbons was obtained as reaction products with these two catalysts, especially in the HDC of TCM, favoring the formation of carbonaceous deposits which provoked a marked deactivation of the catalysts. In contrast, CH4 was the only non-chlorinated product obtained with the Pt/C catalysts which showed by far the highest stability. Different reaction pathways were found depending on the catalyst and the starting chloromethane. The different reactivity of the metals is explained in terms of their different electronic structure and the physicochemical properties of the catalysts.
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    Hydrodechlorination of chloromethanes with Pd on activated carbon catalysts for the treatment of residual gas streams
    (2010) Álvarez-Montero, M.A.; Gómez-Sainero, L.M.; Martín Martínez, María; Heras, F.; Rodriguez, J.J.
    Laboratory-prepared Pd/C catalysts have been investigated in the deep gas-phase hydrodechlorination (HDC) of monochloromethane (CH3Cl), dichloromethane (CH2Cl2) and trichloromethane (CHCl3). The catalysts were found to be active in HDC, the reactivity following the order CHCl3 > CH2Cl2 > CH3Cl. Selectivities to non-chlorinated compounds were found to be higher than 90% in most cases. The results obtained with the catalyst prepared from PdCl2 suggest that all the reaction products are primary products. The CH4, CH3Cl and CH2Cl2 come from the hydrogenation of the corresponding adsorbed chloride radical, while hydrocarbons of more than one carbon atoms are formed by reaction and subsequent hydrodechlorination of two radicals adsorbed in neighbouring active centers. The catalyst undergoes a significant deactivation which appears to be due to the poisoning of active centers with chlorinated hydrocarbons. The use of Pd(NO3)2 as Pd precursor leads to a decrease in the activity due to its lower Pd dispersion and a lower proportion of electrodeficient Pd species.
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    Hydrodechlorination of dichloromethane with mono- and bimetallic Pd–Pt on sulfated and tungstated zirconia catalysts
    (2012) Bedia, J.; Gómez-Sainero, L.M.; Grau, J.M.; Busto, M.; Martín Martínez, María; Rodriguez, J.J.
    Monometallic (Pt or Pd) and bimetallic (Pt–Pd) catalysts supported on zirconia promoted with sulfate (SZ) or tungsten oxide (WZ) were prepared and tested in the gas-phase hydrodechlorination of dichloromethane. The catalysts showed a high selectivity to non-chlorinated products (between 80% and 90% at 250 °C) being methane the main reaction product. As a general trend, the WZ catalysts yielded significantly higher dichloromethane conversion than the SZ ones, yielding all the catalysts initial conversions higher than 80% at a reaction temperature of 250 °C. However, the former showed a very poor stability regardless of the metallic active phase. On the other hand, the presence of palladium in the sulfated zirconia catalyst avoids deactivation as proved in long-term experiments (80-h time on stream). XPS and elemental analyses of the used catalysts suggest that adsorption of organochlorinated species is a cause of deactivation by blocking the active sites. In the monometallic SZ Pt catalyst, deactivation occurs also by poisoning of the Pt sites by the H2S resulting from sulfate reduction under the hydrogen-rich gas atmosphere. The metal particle size appears to be a critical point with regard to stability of the catalysts. The one with the highest dispersion showed the highest stability with no signs of deactivation after more than 80 h on stream.