Angeliki A. Lemonidou

Highly Selective Catalytic Conversion of Phenolic Bio‐Oil to Alkanes

Oil and water: A new energy-efficient and atom-economical catalytic route for the production of alkanes and methanol by upgrading the phenolic fraction of bio-oil has been developed. The one-pot aqueous-phase hydrodeoxygenation process is based on two catalysts facilitating consecutive hydrogenation, hydrolysis, and dehydration reactions.

Towards Quantitative Catalytic Lignin Depolymerization

The products of base-catalyzed liquid-phase hydrolysis of lignin depend markedly on the operating conditions. By varying temperature, pressure, catalyst concentration, and residence time, the yield of monomers and oligomers from depolymerized lignin can be adjusted. It is shown that monomers of phenolic derivatives are the only primary products of base-catalyzed hydrolysis and that oligomers form as secondary products. Oligomerization and polymerization of these highly reactive products, however, limit the amount of obtainable product oil containing low-molecular-weight phenolic products. Therefore, inhibition of concurrent oligomerization and polymerization reactions during hydrothermal lignin depolymerization is important to enhance product yields. Applying boric acid as a capping agent to suppress addition and condensation reactions of initially formed products is presented as a successful approach in this direction. Combination of base-catalyzed lignin hydrolysis with addition of boric acid protecting agent shifts the product distribution to lower molecular weight compounds and increases product yields beyond 85%.

Thermodynamic analysis of hydrogen production via autothermal steam reforming of selected components of aqueous bio-oil fraction

From a technical and economic point of view, autothermal steam reforming offers many advantages, as it minimizes heat load demand in the reformer. Bio-oil, the liquid product of biomass pyrolysis, can be effectively converted to a hydrogen-rich stream. Autothermal steam reforming of selected compounds of bio-oil was investigated using thermodynamic analysis. Equilibrium calculations employing Gibbs free energy minimization were performed for acetic acid, acetone and ethylene glycol in a broad range of temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm) values. The optimal O2/fuel ratio to achieve thermoneutral conditions was calculated under all operating conditions. Hydrogen-rich gas is produced at temperatures higher than 700 K with the maximum yield attained at 900 K. The ratio of steam to fuel and the pressure determine to a great extent the equilibrium hydrogen concentration. The heat demand of the reformer, as expressed by the required amount of oxygen, varies with temperature, steam to fuel ratio and pressure, as well as the type of oxygenate compound used. When the required oxygen enters the system at the reforming temperature, autothermal steam reforming results in hydrogen yield around 20% lower than the yield by steam reforming because part of the organic feed is consumed in the combustion reaction. Autothermicity was also calculated for the whole cycle, including preheating of the organic feed to the reactor temperature and the reforming reaction itself. The oxygen demand in such a case is much higher, while the amount of hydrogen produced is drastically reduced.

Oxidative dehydrogenation of propane over vanadium oxide based catalysts: Effect of support and alkali promoter

The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al2O3 ,T iO 2, ZrO2 and MgO. The promotion of V2O5/Al2O3 catalyst with alkali metals (Li, Na, K) was also attempted. Evaluation of temperature programmed reduction patterns showed that the reducibility of V species is affected by the support acid‐base character. The catalytic activity is favored by the V reducibility of the catalyst as it was confirmed from runs conducted at 450‐550 C. V2O5/TiO2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support’s nature also affects the selectivity to propene; V2O5 supported on Al2O3 catalyst exhibits the highest selectivity. Reaction studies showed that addition of alkali metals decreases the catalytic activity in the order non-doped>Li>Na>K. Propene selectivity significantly increases in the presence of doped catalysts.

Carbon dioxide reforming of methane over 5 wt.% Ni/CaO-Al2O3 catalyst

Methane reforming by carbon dioxide was investigated over 5 wt.% Ni/CaO-Al2O3 catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPR) techniques were applied to characterise the catalyst. The catalyst exhibited high activity and very good stability at stoichiometric methane and carbon dioxide feed. The addition of steam in the reacting mixture was tested and proved beneficial for the conversion of methane and the drastic decrease in carbon deposition. The kinetic behaviour of the catalyst was investigated as a function of temperature and methane and carbon dioxide partial pressures. The apparent activation energies of the two reactants CH4 and CO2 were estimated 25.5 ± 2.0 and 23.6 ± 1.8 kcal/mol, respectively and that of CO was 24.6 ± 1.2 kcal/mol while hydrogen activation energy was estimated at 35.2 ± 3.2 kcal/mol. Partial pressure dependencies of the reaction rates were obtained at 630 ◦ C. The increase of H2 partial pressure resulted in an acceleration of the CO formation, while an increase in CO partial pressure demonstrated the inhibiting role in H 2 formation and the conversion of the reactants.

Investigations on the oxidative dehydrogenation of n-butane over VMgO-type catalysts

The oxidative dehydrogenation of n-butane was investigated over VMgO mixed oxide and pure magnesium ortho- and pyrovanadate catalysts. The formulation containing 30 wt% V2O5 and consisting of the Mg3(VO4)2 and MgO crystal phases is more selective than the pure Mg3(VO4)2, while the Mg2V2O7 phase is the least selective. The selectivity to butenes and butadiene increases with the reaction temperature and the feed molar ratio of butane/oxygen. Addition of water tends to decrease the conversion of butane and enhances the oxydehydrogenation product selectivity. The relative importance of the primary and secondary paths of the reaction network was analyzed by the method of addition of intermediate products. # 1998 Elsevier Science B.V. All rights reserved.

Methane partial oxidation to synthesis gas using nickel on calcium aluminate catalysts

Abstract Nickel was supported on calcium aluminate carriers that were obtained with varying CaO to Al 2 O 3 molar ratios and calcination temperatures. The variations of the supports lead to catalysts of different surface properties and catalytic performance. Metallic nickel (Ni 0 ) was proven to be the active species for the methane partial oxidation reaction. The presence of filamentous carbon on used catalysts was also suggested. The differences in the catalytic activity and selectivity for the methane partial oxidation reaction was ascribed to a varying degree of reducibility of the surface nickel species.

Preparation and evaluation of catalysts for the production of ethylene via steam cracking: Effect of Operating Conditions on the Performance of 12CaO-7Al2O3 Catalyst

Various types of catalyst samples selective for the production of ethylene via steam cracking were prepared. Controlled ratios of two or more oxides and high calcination temperatures were used in order to obtain the desired crystal phases. BET surface-area measurement and X-ray diffraction techniques were used for the examination of the samples. The prepared samples were tested in an experimental pyrolysis unit using n-hexane as a feed. It was found that a catalyst with the formula 12CaO-7Al2O3 has the highest selectivity ratios. The catalyst activity varied widely depending on the operating conditions. At short residence times the catalyst increases the conversion of the feed and hence the olefin yields compared with “inert” α-alumina and thermal cracking (empty reactor). At relatively long residence times and high hydrocarbon partial pressure the catalyst promotes the formation of carbon oxides. Therefore, with a judicious choice of the operating conditions, the catalyst 12CaO-7Al2O3 can act as a steam cracking and/or a steam reforming catalyst. Testing of a sample following treatment with hydrogen at high temperature showed no catalytic activity. It is believed that the increased catalyst activity is due to the excess of oxygen that exists in the crystal phase Ca12Al14O33 of the 12CaO-7Al2O3 catalyst.

Surface properties and reactivity of Al2O3-supported MoO3 catalysts in ethane oxidative dehydrogenation

The effect of MoO3 loading on the properties and the catalytic performance of a series of alumina-supported molybdena catalysts (0–30 wt% MoO3) was investigated in the oxidative dehydrogenation of ethane. The molybdena species on alumina were found to be amorphous at submonolayer coverages. At higher loadings, the formation of Al2(MoO4)3 crystallites was detected by XRD. XPS revealed the existence of both Mo(VI) and Mo(V) sites on the catalyst surface, the concentration of which depends on the MoO3 loading. In terms of catalytic performance, the activity increases with increasing loading in the submonolayer regime, decreasing for higher loadings. High selectivity to ethene is obtained even at relatively high conversion levels for catalysts exceeding monolayer coverage.

One-step propylene formation from bio-glycerol over molybdena-based catalysts

This work presents a novel, one-step catalytic process, enabling highly selective propylene formation via glycerol hydro-deoxygenation (HDO) reactions. Fe–Mo catalysts, supported on black and activated carbons, are selective towards C–O bond cleavage, thus converting glycerol to propylene with high yields. BET, XRD, TPD-NH3 and TPD-He methods have been employed for the characterization of the samples. Molybdenum oxide, at its reduced state, is essential for driving selectively the reaction towards complete deoxygenation. The only product of glycerol HDO is propene, in the gas phase, while 2-propenol, propanols and propylene glycol have been detected, among others, in the liquid phase. Under the standard reaction conditions (300 °C temperature, 8.0 MPa hydrogen pressure), glycerol conversion exceeds 88% and selectivity to propene reaches 76% after 6 hours of reaction. This study includes the investigation of the operating conditions effect (i.e. reaction time, reaction temperature, catalyst loading and H2 pressure) regarding glycerol HDO towards propene formation.