Person: Martín Martínez, María
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First Name
María
Last Name
Martín Martínez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Ingeniería Química y de Materiales
Area
Ingeniería Química
Identifiers
5 results
Search Results
Now showing 1 - 5 of 5
Item 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.Item 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.Item Density functional theory analysis of dichloromethane and hydrogen interaction with Pd clusters: first step to simulate catalytic hydrodechlorination(The Journal of Physical Chemistry C, 2011) Salama Omar; Jose Palomar; Luisa M. Gómez-Sainero; Maria A. Álvarez-Montero; Martín Martínez, María; Juan J. RodriguezA density functional theory (DFT) analysis has been conducted for the gas-phase hydrodechlorination (HDC) of dichloromethane (DCM) with palladium catalyst to achieve a better knowledge of the reaction mechanism involved in the HDC process, which constitutes an emerging technology for the treatment of organochlorinated contaminants. The computational study included the effect of size, oxidation state, and spin configuration of Pd cluster on the adsorption of H2 and DCM reactants on the catalyst surface. Calculations described the activation of H2 by Pd clusters through a dissociative adsorption with low enthalpy values. In addition, partially and fully dissociated DCM intermediates on Pd surface were predicted by DFT calculations. Remarkably, the dissociative adsorption of DCM on Pd active sites occurs via the scission of C–Cl bonds, promoted by the formation of C–Pd linkages, implying high adsorption enthalpy. The computational results showed that DCM can be also molecularly adsorbed on both zerovalent and electrodeficient Pd species. However, the nondissociative adsorption of DCM over electrodeficient Pd cluster is remarkably favored in energy, with adsorption enthalpies (∼−50 kcal/mol) corresponding to chemisorption. Current theoretical evidence explained the deactivation of Pd/AC catalyst as a consequence of the selective poisoning of electrodeficient Pd active centers by chlorinated hydrocarbons, in good agreement with our previous experimental findings.Item 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.Item Removal of chlorinated organic volatile compounds by gas phase adsorption with activated carbon(Chemical Engineering Journal, 2012) Lemus, Jesus; Martín Martínez, María; Palomar, Jose; Gomez-Sainero, Luisa; Gilarranz Redondo, Miguel Ángel; Rodriguez, Juan J.This paper discusses the removal of chlorinated volatile organic compounds (Cl-VOCs) from gas streams by means of fixed-bed adsorption with a commercial activated carbon (AC). Column experiments were performed at different conditions (inlet concentration, temperature, pressure, gas flow rate and bed length). A two-parameter model introduced by Yoon and Nelson was applied to predict the entire breakthrough curves for chloromethane adsorption. Complete regeneration of the exhausted AC was performed at mild conditions (atmospheric pressure and room temperature). In order to gain a better knowledge on the effect of the surface chemistry of AC on the adsorption of Cl-VOCs, the quantum-chemical COSMO-RS method was used to simulate the interactions between AC surface groups and different Cl-VOCs as monochloromethane, dichloromethane and trichloromethane. This information can be useful for tailoring the ACs with the objective of improving their adsorption capacities by further functionalization. To confirm this, the commercial AC tested was modified by means of different thermal and oxidative treatments (nitric acid and ammonium persulfate), being the surface chemistry and textural properties of the resulting materials characterized by different techniques. The modified ACs were then tested in column adsorption experiment with different Cl-VOCs. The uptake of these compounds increased with the basic character of the AC surface.