Marcelo M. Pereira

Synthesis and characterization of niobium oxide layers on silica and the interaction with nickel

Abstract A surface phase oxide containing niobiuma oxide, deposited on non-porous silica was prepared by two different methods. The photoelectron spectroscopy (XPS) and infrared results show that the method using five-stage attaching reactions between Nb(OC2O5)5 and silanol led to a very close one-atomic-layer niobium oxide structure on SiO2. This sample presented two oxygen species comparable to model systems and it was possible to distinguish them in the XPS spectral even when using a silica powder. Cyclohexane dehydrogenation was used to characterize the reduced metallic surface. The nickel compounds interact preferentially with niobia rather than with silica. These nickel species favored lower dehydrogenation activity, suggesting the choice of niobia as a nickel trap.

Rational Design of Microporous and Mesoporous Solids for Catalysis: From the Molecule to the Reactor

Zeolitic materials are the heterogeneous catalysts that have the highest annual production and are used in numerous acid‐catalyzed reactions. Nowadays, hydrocarbon transformations, such as cracking, alkylation, and isomerization, are preferably conducted using these environmentally friendly microporous solid acids. In the general shift from homogeneous towards heterogeneous catalysis, zeolites play a key role. The rational design of these inorganic materials with highly crystalline structure is warranted both in academic and in industrial research. A proper chemical composition, a hierarchical porosity, an appropriate crystal size have, therefore, to be combined with a proper shape at the reactor level.

SMSI effect in the butadiene hydrogenation on Pd-Cu bimetallic catalysts

Abstract Niobla Pd-Cu supported bimetallic catalysts have been studied In the 1,3-butadlene hydrogenation. On catalysts reduced at 573K, the addition of copper to palladium decreased the hydrogen adsorption capacity and the turnover frequency but Increased the trans/cis 2-butene ratio. These results are ascribed to a bimetallic formation. After reduction at 773K. the hydrogen chemlsorptlon and turnover frequency are drastically reduced due to SMSI effect. The 1,3-butadlene hydrogenation seems to be a structure sensitive reaction.

The nickel–niobia–silica interactions at low nickel contents

Abstract Nickel was impregnated in two Nb 2 O 5 /SiO 2 samples. The first one contained small crystallites of niobia dispersed over silica and the second one a niobia monolayer distributed quite uniformly over the silica substrate. These systems were submitted to different treatments (calcination and water vapor) in order to obtain different interactions between the nickel and niobia. A preferential interaction of the nickel with niobia was observed in both niobia–silica samples. The hydrogenation of benzene and dehydrogenation of cyclohexane were used to characterize the reduced surface nickel. Suppression in the catalytic activity was observed due to a strong metal-support interaction (SMSI) and nickel niobate formation. The extension of SMSI and nickel niobate formation depend on the niobia–silica interactions, which are a function of sample preparation and treatment.

Gasoline from Biomass through Refinery-Friendly Carbohydrate-Based Bio-Oil Produced by Ketalization

The introduction of biomass-derived compounds as an alternative feed into the refinery structure that already exists can potentially converge energy uses with ecological sustainability. Herein, we present an approach to produce a bio-oil based on carbohydrate-derived isopropylidene ketals obtained by reaction with acetone under acidic conditions directly from second-generation biomass. The obtained bio-oil showed a greater chemical inertness and miscibility with gasoil than typical bio-oil from fast pyrolysis. Catalytic upgrading of the bio-oil over zeolites (USY and Beta) yielded gasoline with a high octane number. Moreover, the co-processing of gasoil and bio-oil improved the gasoline yield and quality compared to pure gasoil and also reduced the amount of oxygenated compounds and coke compared with pure bio-oil, which demonstrates a synergistic effect.

Nickel activation for hydrogenolysis reaction on USY zeolite

The effects of the SAR (14 and 38) and of the methodology of introduction of nickel (wetness impregnation and ion exchange) on catalyst activation were investigated in Ni/USY model catalysts submitted to two activation treatments: reduction (A) and reduction/calcination/reduction, successively (B). the catalysts prepared by wetness impregnation, a marked increase in the catalytic activity after treatment B was observed. On the basis of the catalyst efficiency toward ethane hydrogenolysis, the lower SAR catalyst presents a threefold higher activity. On the contrary, the catalysts prepared by ion exchange, as well as a model catalyst prepared by wetness impregnation over a USY exhaustively exchanged with nickel ions, do not present measurable increasing of the catalytic activity under the same activation conditions. Monitoring the catalyst activation by EXAFS indicates the formation of nickel clusters in the impregnated catalysts after activation treatment B, which should be responsible for the high catalytic activity. However, TEM images reveal a bimodal particle size distribution, with large (ca. 20 nm) and small nickel particles. Temperature-programmed reduction performed under the same conditions of catalyst activation suggests that only the small nickel particles are activated under the experimental conditions adopted in this work.

Use of Nb2O5 as nickel passivating agent: characterisation of the Ni/Nb2O5/SiO2 system

Abstract Niobia-modified silica was used as support for nickel-based catalysts. Catalysts with different nickel loading were prepared by successive incipient-wetness impregnation of toluenic nickel octanoate solutions. The samples were characterised after both calcination and reduction by TEM-EDX techniques and tested in the ethane hydrogenolysis. Their catalytic behaviour was compared to that of related silica-supported nickel catalysts. A high suppression of hydrogenolysis activity (93–99%) was determined for the niobia-modified silica-supported nickel catalysts which do not show nickel particles on silica.

Cyclohexane as a Probe to Nickel Vanadium Interaction in FCC Catalysts

Abstract Nickel and vanadium were responsible for a great number of deactivation problems in the FCC. To understand their mutual influences, the metals were introduced by incipient wetness impregnation of organometallic compounds onto a highly dealuminated zeolite that had a constant lattice similar to the equilibrium FCC catalyst. Catalyst tests, TPR, DRS and X-ray diffraction were used to characterize the samples. After calcination, the acid sites of the zeolite were poisoned by vanadium without damage to the Crystallinity. Water vapor and high temperature treatment on vanadium/zeolite samples leads to a severe damage of the zeolite framework. The presence of nickel slightly attenuated this problem. The amount of benzene formed was affected by the Ni/V ratio.

Vanadium–Potassium-Alumina Additives for SOx Removal in FCC: Effect of Vanadium Content

The fluid catalytic cracking is one of the main processes responsible for Sulfur emission in a refinery. Herein the effect of vanadium loading over an alumina previously modified with potassium was studied for sulfur mitigation. Vanadium is a key variable and even at very low amount all reaction steps involved in such process were improved.Graphical Abstract

Passivation of nickel activity in the nickel-Nb2O5-SiO2 system at low metal contents

Abstract Niobia/silica systems were used as a nickel trap. A great decrease in the catalytic activity of the cyclohexane reaction (hydrogenolisis and dehydrogenation) was observed, with a remarkable effect on the selectivity. The nickel/silica systems presented a great deal of hydrogenolisis product formation, while the major product on the nickel/niobia/silica surfaces was benzene. Nickel was reimpregnated three times to obtain the limit of passivation. A preferential interaction was observed between the nickel compounds and niobia.