MOLYBDENUM DOPED CARBON AEROGELS WITH CATALYTIC POTENTIAL

Mo-doped carbon aerogels were obtained in the polycondensation reaction of aqueous resorcinol and formaldehyde by adding Mo-salt at two different stages of the synthesis: i) to the initial sol; ii) by incipient wetting impregnation of the supercritically dried polymer gel. Molybdenum added during the polymerization yielded a more compact gel structure with practically no mesoporosity. With post-impregnation, by contrast, mesopores of diameter 3-15 nm were generated. Carbonization appreciably enhanced the microporous character of both samples, but in the mesopore range their pore size distribution was conserved. The Mocontent of the samples was also different: Mo was lost during the solvent exchange before the supercritical drying (i.e., the Mo failed to bind chemically to the polymer matrix). The residual Mo congregated into 25-60 nm bulk clusters of α-Mo2C. In the other carbon aerogel, finely dispersed α-Mo2C and η-Mo3C2 crystals formed, of size 8-20 nm. On the surface of both carbons the Mo formed oxides. In the model test reaction (acetic acid hydroconversion) the catalytic activity of both carbon aerogels was enhanced by molybdenum. The more open pore structure, higher concentration and finer Mo distribution, as well as its chemical form, may all be responsible for the greater conversion and higher value products obtained with the post-impregnated sample

An Aging Model of NH3 Storage Sites for Predicting Kinetics of NH3 Adsorption, Desorption and Oxidation over Hydrothermally Aged Cu-Chabazite

A unified transient kinetic model which can predict the adsorption, desorption and oxidation kinetics of NH3 over hydrothermally aged Cu-chabazite was developed. The model takes into account the variation of fractional coverages of NH3 storage sites due to hydrothermal aging. In order to determine the fractional coverage of these sites, the catalyst was aged for various times at a certain temperature followed by NH3 adsorption, desorption and temperature-programmed desorption (TPD) experiments. TPD profiles were deconvoluted mainly into three peaks with centres at 317, 456 and 526 °C, respectively. Hydrothermal aging resulted in the progressive increase in the intensity of the peak at 317 °C and decrease in the intensity of the peaks at 456 and 526 °C, along with decreased NH3 oxidation at high temperatures. A model for hydrothermal aging kinetics of the fractional coverage of storage sites was developed using three reactions with appropriate rate expressions with parameters regressed from experimental data. The model was then incorporated into a multi-site kinetic model for the degreened Cu-Chabazite by the addition of aging reactions on each storage site. The effects of both aging time and temperature on the kinetics NH3 adsorption, desorption and oxidation were successfully predicted in the 155-540 °C range. This study is the first step towards the development of a hydrothermal aging-unified kinetic model of NH3-Selective Catalytic Reduction over Cu-chabazite

Stepwise conversion of methane to methanol over Cu-mordenite prepared by supercritical and aqueous ion exchange routes and quantification of active Cu species by H2-TPR

Copper-exchanged mordenite prepared by supercritical ion exchange (SCIE) and aqueous ion exchange (AIE) were investigated in stepwise conversion of methane to methanol. Increasing the oxygen activation temperature and methane reaction time enhances the methanol yield of copper-exchanged mordenite prepared by SCIE (Cu-MORS). The reducibility of Cu-MORS was compared with those of Cu-MORA prepared by aqueous ion exchange (AIE) using H2-TPR. It was demonstrated for the first time that deconvoluted H2-TPR profile coupled with effects of Cu loading and oxygen activation temperature on methanol yield data can be used to distinguish the active Cu sites from inactive ones based on their reduction temperature. The copper species responsible for methane activation were found to be reduced below 150 °C by H2 in both Cu-MORS and Cu-MORA. From the stoichiometry of the reaction of H2 with Cu2+ species, the average number of copper atoms of active sites were calculated as 2.07 and 2.80 for Cu-MORS and Cu-MORA, respectively. Differences in structure of copper species caused by the synthesis routes were also detected by in-situ FTIR upon NO adsorption indicating a higher susceptibility of Cu-MORS towards autoreduction. The results demonstrated the potential of TPR based methods to identify copper active sites and suggested the importance of site selective ion exchange in order to controllably synthesize active Cu species in zeolites.ISSN:1566-7367ISSN:1873-390

A Promising Catalyst for the Dehydrogenation of Perhydro-Dibenzyltoluene: Pt/Al₂O₃ Prepared by Supercritical CO₂ Deposition

Pt/Al2O3 catalysts prepared via supercritical deposition (SCD), with supercritical CO2, wet impregnation (WI) methods and a selected benchmark catalyst, were evaluated for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT) at 300 °C in a batch reactor. After ten dehydrogenation runs, the average performance of the catalyst prepared using SCD was the highest compared to the benchmark and WI-prepared catalysts. The pre-treatment of the catalysts with the product (dibenzyltoluene) indicated that the deactivation observed is mainly due to the adsorbed H0-DBT blocking the active sites for the reactant (H18-DBT). Furthermore, the SCD method afforded a catalyst with a higher dispersion of smaller sized Pt particles, thus improving catalytic performance towards the dehydrogenation of H18-DBT. The particle diameters of the SCD- and WI-prepared catalysts varied in the ranges of 0.6–2.2 nm and 0.8–3.4 nm and had average particle sizes of 1.1 nm and 1.7 nm, respectively. Energy dispersive X-ray spectroscopy analysis of the catalysts after ten dehydrogenation runs revealed the presence of carbon. In this study, improved catalyst performance led to the production of more liquid-based by-products and carbon material compared to catalysts with low catalytic performance

КОЛИЧЕСТВЕННОЕ СРАВНЕНИЕ ГЕОМЕТРИИ МОЛЕКУЛ ПОЛИМОРФНЫХ МОДИФИКАЦИЙ В МОНОКЛИДНОЙ И ТРИКЛИННОЙ СИНГОНИЯХ МЕДИ (II) БИ(1,1,1,3,5,5,6,6,6-НОНАФТОРОГЕКСАН-2,4-ДИИМИНАТА)

This paper presents the results of the complete X-ray structure analysis of Cu[CF3-C(NH)-CF-C(NH)-CF3]2 (CuDI6). Crystals were discovered in triclinic space group. Z = 2 (two independent molecules in asymmetric unit (β_1, β_2)). Final R-factor is 0.1002. A quantitative comparison of the geometry of molecules in two modifications of the triclinic space group with each other and with the geometry of the molecule in the monoclinic (α), which was already obtained earlier [1], is given.В данной работе приводятся результаты рентгено-структурного анализа Cu[CF3-C(NH)-CF-C(NH)-CF3]2 (CuDI6). Были обнаружены кристаллы в триклинной сингонии. Z=2 (две молекулы располагаются независимо в ассиметричной единице ( β 1 , β 2 )). Финальный R-фактор составляет 1,002. Приведено количественное сравнение геометрии молекул в двух модификациях триклинной сингонии между собой и с геометрией молекулы в моноклинной ( α ), которая уже была получена ранее [1]

Electrochemical performance of fuel cell catalysts prepared by supercritical deposition: Effect of different precursor conversion routes

Supercritical deposition (SCD) is used to prepare carbon-supported Pt nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me(2)) is adsorbed from supercritical carbon dioxide (scCO(2)) solutions onto Vulcan VX-72 at 13.2 MPa and 50 degrees C. The adsorbed metal precursor is converted to its metal form via three different routes: thermal conversion in N-2 at ambient pressure (route 1), thermal conversion in scCO(2) (route 2), or chemical conversion in H-2 at ambient pressure (route 3). Sequential SCD is used in routes 1 and 3. The mean diameters of the synthesized Pt nanoparticles are smallest for route 1 and largest for route 3. Nano-scale morphology of the electrocatalysts is characterized using transmission electron microscopy (TEM), revealing narrower Pt particle size distributions for the catalyst prepared via route 1 than for those synthesized by routes 2 and 3. Electrocatalyst prepared using route 1 showed the best performance both in specific activity (measured via cyclic voltammetry) and in PEMFC tests among electrocatalysts prepared using different routes. (C) 2014 Elsevier B.V. All rights reserved

A Promising Catalyst for the Dehydrogenation of Perhydro-Dibenzyltoluene: Pt/Al2O3 Prepared by Supercritical CO2 Deposition

Pt/Al2O3 catalysts prepared via supercritical deposition (SCD), with supercritical CO2, wet impregnation (WI) methods and a selected benchmark catalyst, were evaluated for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT) at 300 °C in a batch reactor. After ten dehydrogenation runs, the average performance of the catalyst prepared using SCD was the highest compared to the benchmark and WI-prepared catalysts. The pre-treatment of the catalysts with the product (dibenzyltoluene) indicated that the deactivation observed is mainly due to the adsorbed H0-DBT blocking the active sites for the reactant (H18-DBT). Furthermore, the SCD method afforded a catalyst with a higher dispersion of smaller sized Pt particles, thus improving catalytic performance towards the dehydrogenation of H18-DBT. The particle diameters of the SCD- and WI-prepared catalysts varied in the ranges of 0.6–2.2 nm and 0.8–3.4 nm and had average particle sizes of 1.1 nm and 1.7 nm, respectively. Energy dispersive X-ray spectroscopy analysis of the catalysts after ten dehydrogenation runs revealed the presence of carbon. In this study, improved catalyst performance led to the production of more liquid-based by-products and carbon material compared to catalysts with low catalytic performance