Chloroform conversion into ethane and propane by catalytic hydrodechlorination with Pd supported on activated carbons from lignin

Conversion of chloroform (TCM) by gas-phase catalytic hydrodechlorination (HDC) has been addressed to maximize the selectivity to ethane and propane. Several own-made Pd (1 wt%) catalysts have been tested. The catalysts were prepared by incipient wetness impregnation of five different activated carbons. These carbons were obtained by chemical activation of lignin with different activating agents, namely, H3PO4, ZnCl2, FeCl3, NaOH and KOH. The catalysts were fully characterized by N2 adsorption–desorption at −196 °C, CO2 adsorption at 0 °C, TPR, NH3-TPD, XRD, XPS and TEM. The activating agents provided important differences in the characteristics of activated carbon supports, and hence in the resulting catalysts, in terms of their porous texture, surface acidity, Pd oxidation state and Pd particle size distribution. NaOH and KOH activation led to carbons with the highest surface areas (2158 and 2991 m2 g−1 , respectively) and low Pd0 / Pdn+ ratios, while ZnCl2- and H3PO4-activated carbons yielded the highest surface acidity and mean Pd particle sizes. The analysis of the TOF values revealed that the HDC of TCM on these catalysts is a structure-sensitive reaction, increasing TOF values with Pd particle size. The best results, in terms of selectivity to ethane and propane, were obtained with the catalysts supported on KOH- and NaOH-activated carbons. The former allowed 80% selectivity to the target compounds at almost complete dechlorination (>99%) at 300 °C. The KOH-based catalyst showed fairly good stability at a reaction temperature of 200 °CThe authors gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) through the project CTM 2014-5300

Gas-phase hydrodechlorination of mixtures of chloromethanes with activated carbon-supported platinum catalysts

Platinum catalysts supported on activated carbon (Pt/C) at different metal loadings (0.5-2% Pt) have been tested in the gas-phase hydrodechlorination (HDC) of mixtures of dichloromethane (DCM) and chloroform (TCM), with a total feed concentration of 1000ppmv. Almost complete dechlorination was achieved at 250°C, 1kghmol-1 space time and a H2/CM molar ratio of 25 with the 2% Pt catalyst. At a reaction temperature of 250°C, scarce inhibition in the conversion of both compounds was observed compared to the HDC of the individual chloromethanes. The TOF values for DCM increase with the Pt content, which can be attributed to the higher proportion of the zero-valent species. The selectivity to reaction products suggests a parallel reactions scheme. The catalysts showed a high stability, demonstrated by the unchanged conversion of both chloromethanes upon time on stream in long-term experiments carried out at up to 26h.The authors gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) through the project CTM2011-2835

Effect of the Pt–Pd molar ratio in bimetallic catalysts supported on sulfated zirconia on the gas-phase hydrodechlorination of chloromethanes

Bimetallic Pt:Pd catalysts with different molar ratios and 0.5 wt.% overall metal load supported on sulfated zirconia catalysts were synthesized and tested in the gas-phase hydrodechlorination (HDC) of chloromethanes and their mixtures. The catalysts were characterized by adsorption–desorption of N2 at −196 °C, X-ray diffraction, X-ray photoelectronic spectroscopy, temperature-programmed reduction, and aberration-corrected scanning transmission electron microscopy (STEM). The effect of the Pt:Pd molar ratio on the activity, stability, and selectivity was analyzed. The high acidity of the sulfated zirconia results in metal particles of small size (mainly <5 nm), as confirmed by STEM. The bimetallic catalysts showed higher stability than the monometallic ones, as demonstrated in long-term experiments (80 h on stream), confirming the positive effect of combining the two metallic phases. Turnover frequency (TOF) values in the range 0.0007–0.0168 s−1 and apparent activation energies between ≈41 and 44 kJ·mol−1 were obtained. TOF values for dichloromethane HDC increased with increasing mean metal particle size within the range of this work (≈1.2–2.3 nm). The catalysts with Pt:Pd molar ratios of 1:3 and 1:1 showed significantly better performance than the 3:1 one for overall dechlorination due to their higher atomic metal content and TOF at the same total metal weight load (0.5%)The authors are grateful to the Spanish ‘‘Ministerio de Economíay Competitividad (MINECO)” for financial support (ProjectsCTM2011-28352 and CTM2014-53008-

Selectivity to Olefins in the Hydrodechlorination of Chloroform with Activated Carbon-Supported Palladium Catalysts

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial & Engineering Chemistry Research, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acs.iecr.9b04262The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.9b04262This study analyzes the selectivity of Pd (1 wt %) catalysts supported on different activated carbons to produce olefins from hydrodechlorination of chloroform. It was found that selectivity to olefins was favored by a higher zerovalent to electrodeficient Pd ratio (Pd0/Pdn+) and by a lower amount of oxygen-containing surface functional groups on the activated carbon supports. Thus, the highest selectivity to olefins was obtained by catalysts supported on FeCl3- and ZnCl2-activated carbons. Conversely, the catalysts supported on KOH-, NaOH-, and H3PO4-activated carbons gave the lowest selectivity to olefins. These catalysts showed higher surface concentrations of electro-deficient Pd as well as high concentrations of oxygen functional groups that enhance the adsorption of reactants and intermediates. This leads to complete hydrogenation of reaction intermediates and poisoning of active sites by the adsorption of chlorocarbon compounds. ZnCl2-derived catalysts with the highest selectivity to olefins also showed an outstanding stability, most likely due to redispersion into very small and well-distributed Pd particles during the reaction. However, FeCl3-derived catalysts gave rise to sintering of Pd particles, resulting in a marked loss of activityAuthors acknowledge financial support from FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación/CTM2017-85498-R. C. Fernández Ruiz acknowledges MINECO for his research grant. S. Andreoli acknowledges the fellowship received from the “Toso Montanari” Foundation, University of Bologn

Effect of barium and lanthanum oxides on the properties of Pt/KL catalysts in the n-heptane dehydrocyclization

Six fractions of zeolite KL were impregned with 1, 3 and 5 wt% of Ba or La, respectively, with nitrate precursors aqueous solutions. After calcination at 873 K to form BaO or La2O3, 1 wt% of Pt was incorporated to the supports by the impregnation method. Metal dispersion decreases as the Ba concentration increases, but it is not substantially affected by the La addition. The CO/FTIR and the competitive hydrogenation of benzene + toluene results indicate that an electron enrichment of the Pt particles occurs by effect of the additives. The increase of the electron density of Pt in Ba-catalysts is higher than for the La-catalysts. Moreover, the Ba addition highly enhances the aromatization and terminal hydrogenolysis activities, without substantial modification of the yields to the other reaction products. The yield to toluene is also increased by effect of 1 wt% of La, but it does not increases with the La concentration. The TEM-EDX studies indicate that the different distribution of the BaO and La2O3 in the zeolite may be the origin of the different surface and catalytic effects of these oxides in the Pt/KL catalysts.Fil: Grau, Javier Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina. Universidad Autónoma de Madrid; EspañaFil: Gómez Sainero, L. M.. Universidad Autónoma de Madrid; EspañaFil: Daza, L.. Universidad Autónoma de Madrid; EspañaFil: Seoane, X.L.. Universidad Autónoma de Madrid; EspañaFil: Arcoya, A.. Universidad Autónoma de Madrid; Españ

Enhanced selectivity to olefins in the hydrodechlorination of trichloromethane using Ag-Pd on activated carbon catalysts

Two Ag-Pd (nominal 1 % wt each) bimetallic catalysts supported on commercial activated carbon were synthesized and tested, for the first time, in the hydrodechlorination (HDC) of trichloromethane (TCM) to obtain light olefins. Two different Pd precursors were used, PdCl2 and Pd(NO3)2, being the resulting catalysts denoted as AgPdCl/C and AgPdN/C, respectively. A monometallic Ag catalyst was also prepared for comparison purposes. The two different Pd precursors led to different metal particle sizes and zerovalent to electrodeficient metal ratios. The monometallic Ag catalyst showed a poor dechlorination, in contrast with the bimetallic ones. AgPdN/C yielded high selectivity to paraffins, while AgPdCl/C was more selective to olefins (mostly ethylene), the desired reaction products. This better behavior of AgPdCl/C in terms of selectivity to ethylene and propylene was probably due to the existence of smaller Pd nanoparticles as monometallic sites. These Pd sites are active for the conversion of chloromethanes into light unsaturated hydrocarbons, while larger Pd clusters present higher hydrogenation ability. AgPdCl/C allowed complete TCM conversion, with high overall dechlorination and outstanding 75 % selectivity to olefins, showing very high stability at a reaction temperature of 350 °C for almost 35 h on stream. These results represent a significant improvement respect to those obtained with monometallic Pd on activated carbon catalysts reported in our previous studies. To the best of our knowledge, for the first time it is reported such high selectivity to olefins as the above indicated from HDC of a chloromethaneAuthors acknowledge financial support from FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación/ CTM2017-85498-R. C. Fernández Ruiz acknowledges MINECO for his research gra

Hydrogen production by reforming of methanol with Pd/CeO₂-Sm₂O₃ catalysts

The behavior of two 2% Pd/Sm2O3-CeO2 catalysts with the support calcined at different temperatures in the reforming of methanol was studied to be used as electro-catalysts in Direct Methanol Intermediate Temperature Solid-Oxide Fuel Cell. Activity measurements were performed in a fixed bed micro-reactor using 0.1 g of catalyst at 1 atm, 400°C, space velocity of 0.32 mole/hr-g cat, H2O/CH3OH molar ratio = 1.2:1 and a methanol concentration in the gas stream of 15 mole %. The catalyst with the support calcined at 800°C (Pd/CS-800) was considerably more efficient for H2 production. A thicker layer of Sm2O3 decorating CeO2 particles was observed in Pd/CS-1000, which led to a stronger interaction with the Pd particles, so hindering its spread into the support and making them more inaccessible to the gas atmosphere. A better Pd dispersion and a more homogeneous distribution in the surface of Sm2O3 was found. This is an abstract of a paper presented at the 8th World Congress of Chemical Engineering (Montréal, Quebec, Canada 8/23-27/2009).</p

Hydrogen production by reforming of methanol with Pd/CeO₂-Sm₂O₃ catalysts

The behavior of two 2% Pd/Sm2O3-CeO2 catalysts with the support calcined at different temperatures in the reforming of methanol was studied to be used as electro-catalysts in Direct Methanol Intermediate Temperature Solid-Oxide Fuel Cell. Activity measurements were performed in a fixed bed micro-reactor using 0.1 g of catalyst at 1 atm, 400°C, space velocity of 0.32 mole/hr-g cat, H2O/CH3OH molar ratio = 1.2:1 and a methanol concentration in the gas stream of 15 mole %. The catalyst with the support calcined at 800°C (Pd/CS-800) was considerably more efficient for H2 production. A thicker layer of Sm2O3 decorating CeO2 particles was observed in Pd/CS-1000, which led to a stronger interaction with the Pd particles, so hindering its spread into the support and making them more inaccessible to the gas atmosphere. A better Pd dispersion and a more homogeneous distribution in the surface of Sm2O3 was found. This is an abstract of a paper presented at the 8th World Congress of Chemical Engineering (Montréal, Quebec, Canada 8/23-27/2009).</p