n-Heptane hydroconversion over nickel-loaded aluminum- and/or boron-containing BEA zeolites prepared by recrystallization of magadiite varieties

Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py), ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift towards isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption

The SCR of NO with CH4 over Co-, Co,Pt-, and H-mordenite catalysts

The catalytic reduction of NO with methane was studied operando in the presence and absence of oxygen in the reaction mixture over Co-, Co,Pt-, and H-mordenite (CoM, CoPtM, HM) catalysts using the coupled methods of diffuse reflectance infrared Fourier-transform spectroscopy and mass spectroscopy (Operando-DRIFTS-MS). The reaction temperature was in the 573-773 K range, and the GHSV for nitric oxide was varied between 6000 and 60,000 h-1. In general, the Co-containing mordenite catalysts were more active than the HM. Over each catalyst two major surface intermediates were identified such as nitrosonium ion (NO+) and ammonia. The NO+ cations were shown to balance the negative charge on the zeolite framework. The NH3 molecules were bound either coordinately to Lewis-acid site Co2+ ions or were protonated on Brønsted acid sites and retained by the zeolite as NH4 + cations. The prevailing route of N2 formation was found to involve the reaction of NO+ and NH3 or NH4 + surface species. It was shown that the surface concentration of the intermediate ammonia governed the rate of NO conversion. If O2 was present in the feed gas it competed with the NO in the oxidation of methane and the surface intermediate ammonia. As a result, the steady-state concentration of the ammonia intermediate and the overall NO conversion to N2 decreased. Additional routes of N2 formation were revealed over the CoM and CoPtM catalysts. The cobalt facilitated the formation of NO+ and surface nitrate (NO3 -). Also nitrile (CN) and isocyanate (NCO) surface species were detected. The NO3 - could be rapidly reduced by methane to intermediate NH3 and, thereby, it increased the rate of NO conversion significantly. Nitrogen forming reactions can pass also through CN and NCO intermediates; however, the share of these reaction routes in the overall N2 generation process was minor.Fil: Lónyi, F.. Chemical Research Center, Budapest;Fil: Valyon, J.. Chemical Research Center, Budapest;Fil: Gutierrez, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Ulla, Maria Alicia del H.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Lombardo, Eduardo Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentin