Giuseppe Fornasari

On the Chemistry of Ethanol on Basic Oxides: Revising Mechanisms and Intermediates in the Lebedev and Guerbet reactions

A common way to convert ethanol into chemicals is by upgrading it over oxide catalysts with basic features; this method makes it possible to obtain important chemicals such as 1-butanol (Guerbet reaction) and 1,3-butadiene (Lebedev reaction). Despite their long history in chemistry, the details of the close inter-relationship of these reactions have yet to be discussed properly. Our present study focuses on reactivity tests, inu2005situ diffuse reflectance infrared Fourier transform spectroscopy, MS analysis, and theoretical modeling. We used MgO as a reference catalyst with pure basic features to explore ethanol conversion from its very early stages. Based on the obtained results, we formulate a new mechanistic theory able to explain not only our results but also most of the scientific literature on Lebedev and Guerbet chemistry. This provides a rational description of the intermediates shared by the two reaction pathways as well as an innovative perspective on the catalyst requirements to direct the reaction pathway toward 1-butanol or butadiene.

Vanadium mixed oxide catalysts for the oxidative coupling of methane

Abstract The improvement of methane conversion and C2+ selectivity for the oxidative coupling of methane has been pursued by evaluating a series of new polyfunctional oxide catalysts. The catalysts included: (i) a transition metal oxide, (ii) an alkaline earth metal oxide (CaO or MgO), and (iii) an inert oxide support (Al2O3, SiO2, TiO2, or ZrO2) to stabilize the active phases. Vanadium oxide was chosen from the set of transition metal oxides having a standard free energy change lower than zero for the reaction methane+metal oxide→1/2 ethene+water+reduced metal oxide. The molar composition of the catalysts was the following: 68Mg(Ca)/2V/30Al(Ti, Si, Zr). Several catalysts were tested before and after alkali impregnation (lithium with MgO and sodium with CaO). Impregnation of alkali caused an increase in the methane conversion in the CaO-based catalysts. The catalysts were examined by electron spin resonance and UV-visible spectroscopy to find relationships between vanadium species and catalytic activity. The spectroscopic analyses did not show a correlation between VIV species and catalytic activity, whereas the (V = O)3+ species seems to play an important role in the reaction.

The reducibility of highly stable Ni-containing species in catalysts derived from hydrotalcite-type precursors

A study was conducted on the speciation and reducibility of Ni in catalysts derived from hydrotalcite-type (HT) precursors intercalated by silicates. Silicate and nickel contents in Ni/Mg/Al HT precursors varied and the products obtained by thermal decomposition in the 773–1373 K range were characterized. Sample properties were related to the amount of silicates and nickel. The former altered the formation of the spinel-type phase and decreased the ratio between MgO and MgAl2O4 phases in which the active species were stabilized. On the other hand, the Ni distribution depended on the Ni-loading. Ni-containing species in the spinel phase were more abundant for high Ni-loaded catalysts, and were readily reduced by H2 treatment at 1023 K, whereas those in the Ni1−xMgxO solid solution remained partially unreduced.

Carbonates as reactants for the production of fine chemicals: the synthesis of 2-phenoxyethanol

The solventless and heterogeneously catalysed synthesis of 2-phenoxyethanol (ethylene glycol monophenyl ether) via the reaction between phenol and ethylene carbonate was investigated using Na-mordenite catalysts as an alternative to the industrial process using ethylene oxide and homogeneous basic conditions. Under specific reaction conditions, it was possible to obtain total selectivity to phenoxyethanol at up to 75% phenol conversion and 82% selectivity at total phenol conversion in 5–7 hours of reaction time and using a moderate excess of ethylene carbonate. The main by-product was the linear carbonate of phenoxyethanol, bis(2-phenoxyethyl)carbonate (selectivity 15%), which could then be converted to phenoxyethanol by reacting with phenol in basic medium with 100% yield; so overall, the phenoxyethanol yield was as high as 97%. With a stoichiometric feed of phenol and ethylene carbonate, the maximum conversion of phenol was just 60%, still with 100% selectivity to phenoxyethanol. An autocatalytic phenomenon was also observed due to the higher basicity of 2-phenoxyethanol compared to phenol, which overlapped the Na-catalyzed activation of phenol. Starting from a commercial Na-mordenite, which showed significant deactivation, and by applying a post-treatment aimed at the reduction of microporosity, it was possible to minimize both the deactivation and Na leaching while keeping the selectivity enhancement effect shown by the mordenite structure.

One-step electrodeposition of Pd–CeO2 on high pore density foams for environmental catalytic processes

Environmental catalytic processes are probably the best example for the application of structured catalysts based on activated open-cell metallic foams, and Pd/CeO2 based materials are one of the most active catalysts for different applications like three-way catalysts, methane combustion and water gas shift. Here, we report the one-step deposition of Pd and CeO2 on FeCrAlloy foams with very high pore densities (cell sizes equal to 580 and 1200 μm) by the electro-base generation method followed by calcination. The type of Pd and CeO2 species, the quality of the coating and the catalytic activity in the mass transfer limited CO oxidation as a model reaction were investigated. For comparison purposes, a CeO2 coating was also prepared. Reproducible and evenly distributed defective nano-CeO2 coatings containing PdxCe1−xO2−δ solid solution and Pd0 particles were electrodeposited in 500 s regardless of the foam pore size. The structure, morphology, and adhesion of the catalytic layer, as well as the Pd distribution, were almost constant after calcination at 550 °C, only some PdO segregated. The resulting structured catalysts showed high activity and stability after 48 h time-on-stream and different thermal cycles in CO oxidation even at high GHSV values (e.g. 4 × 106 h−1 referred to as the total foam disk volume). High volumetric mass transfer coefficients, widely outperforming those of conventional honeycomb monoliths, were obtained, especially for the small pore (580 μm) foam. The in situ formation of Pd0 nanoparticles and the homogeneous distribution and stability of the coating may contribute to the high catalytic performance, although these catalyst features depended on the position in the catalytic bed.