Stefano Rossini

The impact of catalytic materials on fuel reformulation

Abstract Fuel reformulation has been seeded by the growing consciousness of the potential damages mankind was causing to the ecosystem and to itself. Fuel reformulation means that fuels are defined on a chemical composition base with additional engine-technology related standards rather than on pure performance bases. These standards, which are getting more and more stringent, can be met by different leverages, mainly catalysts and processes operating conditions. This survey reviews the contribution of catalytic materials to the production of cleaner fuel components through some significant examples selected from scientific and technical literature. Having described the trends in automotive fuels quality, production of gasoline and diesel pool components is discussed relating the required properties to the material active site configuration, i.e. acidity/basicity, structural parameters, physical constraints. While distinctions are made between pathways leading to gasoline and those leading to diesel, sulfur removal is faced on a more generalized approach.

IR study of alkene allylic activation on magnesium ferrite and alumina catalysts

The interaction of propene and butenes with a butene oxydehydrogenation catalyst, MgFe2O4, and with an isomerization catalyst, γ-Al2O3, have been studied by FTIR spectroscopy. Allyloxy species (prop-2-en-1-oxides from propene and but-3-en-2-oxide from but-1-ene) were observed over MgFe2O4, while allyl species (prop-2-en-1-yl from propene, but-3-en-2-yl from but-1-ene and 2-methylprop-2-en-1-yl from isobutene), thought to be σ-bonded to Al3+ ions, were observed over γ-Al2O3. It is proposed that in all cases the allylic C—H bond is heterolytically broken at cation–anion couples (Mn+O2–) to give rise to anionic allyls. However, when the cation is reducible, as on the Fe3+ centres of magnesium ferrite, the allyl anion is further rapidly oxidized to allyloxy species that, at high temperature, can act as cationic allyls which interact weakly with oxide anions. From propene, the cationic allyls can act as symmetric species, as is expected for acrolein synthesis.

An FT-IR and flow reactor study of the conversion of propane on γ-Al2O3 in oxygen-containing atmosphere

Abstract The conversion of propane in the presence of oxygen over alumina has been studied using a fixed bed flow reactor. The interaction of the same catalyst with propane, propene, isopropanol and acetone has also been investigated, with additional gas-phase monitoring, in an FT-IR cell. Alumina looks active in the catalytic conversion of propane to propene, with the production of CO 2 , CO, ethylene, methane as the main by-products, depending on the reaction temperature. Higher hydrocarbons such as butenes, butadiene, benzene and toluene are also found. This reactivity is mainly attributed to the weak but not negligible Bronsted acidity of the surface OH’s of alumina, possibly activating propane in the form of isopropoxides and allowing oligomerization of propene. This shows the detrimental effect of the uncovered alumina support in the case of alumina-supported catalysts for propane oxydehydrogenation and explains the positive role of doping with basic neutralizing agents such as potassium.

FT-IR characterization of silicated aluminas, active olefin skeletal isomerization catalysts

Abstract The surface structure of silicated aluminas, very good as catalysts for n-butene isomerization to isobutene, has been investigated by FT-IR spectroscopy of the silicate species, of the surface hydroxy-groups and of adsorbed pyridine. It has been concluded that silication results in the formation of a surface spinel phase where silicon substitutes for aluminum in tetrahedral sites. This phase exposes surface silanol groups that are not Bronsted acidic enough to protonate pyridine at room temperature. The increase in activity without loss in selectivity to isobutene is mainly attributed to the increased surface hydroxy-group concentration arising from silication, occurring without an increase in Bronsted acidity that would result in loss of selectivity and fast deactivation.

Mesoporous catalysts for the synthesis of clean diesel fuels by oligomerisation of olefins

Abstract Si/Al MCM-41 type mesoporous compounds, as such or containing small amounts of metal (Ni, Rh or Pt), were investigated in the synthesis of clean diesel fuels by oligomerisation of orphan olefin streams. Very good catalytic performances were obtained with C 4 and C 5 olefins, while almost no conversion occurred with ethylene. The activity increased with increasing reaction pressure, temperature and contact time, while high Si/Al ratios had a negative effect on both activity and catalyst stability. The presence of small amount of metal inside the mesoporous structure did not significantly modify the catalytic activity, although specific effects were detected for each element. Since the evaluation of the cetane number by H-NMR gave rise to values about 20% lower than the actual value, a new and more complex algorithm is proposed to calculate the cetane number. Using the proposed algorithm, a good correlation index was found between calculated and motor values for pure compounds. Further study is necessary to move from pure compounds to experimental mixtures.

Propane oxydehydrogenation over alumina-supported vanadia doped with manganese and potassium

Abstract The oxidation of propane over alumina-supported V–Mn–K oxide catalysts has been investigated. The addition of K to vanadia–alumina decreases activity but increases significantly the selectivity to propene. This was found to be due to the poisoning of the acid sites of the alumina support, that convert propene in a number of organic byproducts. Conversely, the addition of Mn decreases both activity and selectivity. In both cases the coordination state of vanadyl sites is perturbed with an increase of the crystal field. FT-IR mechanistic studies support the idea that isopropoxides are intermediates in the formation of propene by propane oxydehydrogenation.

Oxidation of ethane over vanadia-alumina-based catalysts: co-feed and redox experiments

Abstract The conversion of ethane in mixture with oxygen and helium (or air) over a V2O5/Al2O3 12:88 (w/w) and a V2O5-K2O/Al2O3 12:6:82 (w/w) catalysts has been studied. Results of co-feed experiments (with ethane–oxygen–He and with ethane–air feeds) and redox experiments, performed feeding pure ethane over fully oxidized catalysts, have been compared. Data concerning propane conversion over the same catalysts have also been considered. Over the heavily K-doped sample a direct combustion way to CO2 parallel to the oxydehydrogenation way to ethylene is likely to exist. On the contrary, over undoped vanadia-alumina the main combustion way is successive and mainly gives CO. Similar yields have been obtained but at lower temperatures for co-feed than for redox experiments. However, in similar conditions the productivities can be definitely higher in redox than in co-feed experiments. Nevertheless the conversion of ethane in the empty reactor gives rise to definitely higher selectivities and yields, although at very high temperatures, than the catalyzed reactions.

A FT-IR study of the adsorption of C5 olefinic compounds on NaX zeolite

Abstract The IR spectra of 1-pentene, 2-methyl-1-butene, 2-methyl-2-butene and isoprene (2-methyl-1,3-butadiene) liquid and adsorbed on NaX zeolite have been recorded. Empirical assignments for the observed spectrum (4000–1200 cm −1 ) are reported in all cases. Data on the adsorption of water, acetonitrile and C5 alkanes on NaX are also briefly discussed. The behaviour of NaX zeolite in the separation of alkenes from alkanes in selective adsorption processes is also briefly discussed.

One-Step-Hydrogen: a new direct route by water splitting to hydrogen with intrinsic CO2 sequestration

Publisher Summary The One-Step-Hydrogen process is aimed to produce hydrogen from water splitting and also to tackle the carbon management issue targeting a zero carbon emission at lower costs than allowed by the Best Available Technologies (BAT). Well known water possesses an oxidizing potential which can be utilized in a simple water splitting application where it reacts with selected metals to give pure hydrogen. So combining in a cycle the water oxidative potential and the reverse action by a reducing agent like hydrocarbons, it allows the hydrogen production and as well as the intrinsic carbon dioxide sequestration. This chapter proposes this new process. In the first step, a suitable oxide takes up the oxygen from water splitting producing hydrogen. The solid acts as an oxygen storage medium. Such “lattice” oxygen is in turn released through one or more elemental steps. The overall reaction is endothermic and an energy supply is needed to close the energy balance. The decoupling of the overall reaction into three separated reactions allows the process to overcome the thermodynamics constraints of the overall equilibrium. The major breakthrough is however the exit of the two main products—hydrogen and carbon dioxide—from two different vessels, so that the carbon dioxide, once water is condensed, is pure and ready to be buried.

General Mechanism for the oxidative coupling of methane

A detailed mechanism, composed of 27 reactions, for the oxidative coupling of methane is described. The main products may derive either from a surface route or from a gas phase pathway. The kinetic parameters of the model, handled by a computer program, have been calculated from general chemical laws. The proposed mechanism has been calibrated on the data of the Li/MgO catalyst, studied by Lunsford and co-workers. The key steps are discussed in details and the fair good agreement between calculated and experimental data is given.