A series of Al-SBA-15 catalysts in a wide compositional range (Si/Al=130-5.2) was prepared by “pH-adjusting” aiming to evaluate the effect of aluminium incorporation on their structural, acidic and catalytic properties. The calcined materials were characterized by ICP, XRD, N2 adsorption/desorption, TEM, 27Al MAS NMR, microcalorimetry of ammonia adsorption and FTIR of adsorbed pyridine. It was found that the progressive incorporation of aluminium in SBA-15 has a positive effect on the structural and textural characteristics of catalysts as well as on the number of Brönsted and Lewis acid sites, whereas no net effect was observed on the relative distribution of acid sites according to their nature or strength. The catalytic properties of mesoporous SBA-15 aluminosilicates were finally evaluated by test-reactions in the liquid phase tert-butylation of phenol and isomerization of styrene oxide, under mild conditions. The catalytic results showed that the progressive incorporation of aluminium results in higher reaction rates in the O- and C-alkylation of phenol as well as isomerization of styrene oxide, providing evidence that the number of acid sites controls the catalytic activity of Al-SBA-15. On the other hand, the incorporation of aluminium had no effect on the selectivity to the reaction products, indicating that selectivity levels are controlled by the relative distribution of acid sites. It was also reported that Al-SBA-15 prepared by “pH-adjusting” are highly active catalysts in the isomerization of styrene oxide and very selective to phenylacetaldehyde.

In the presence of methyl acetate triglycerides such as vegetable oils are transformed simultaneously into the corresponding fatty acid methyl esters and triacetyl glycerol (triacetin). The reaction, catalyzed by lipases, was studied as a function of some critical parameters, such as type of catalyst, enzyme hydration and immobilization support. The aim of the work was to achieve a conversion of the triglyceride as high as possible and to maximize the yield of the triacetin, the reaction end point. It was found that by using the immobilized lipase from Candida antarctica yields as high as 80% of both fatty acid esters and triacetin could be achieved. These results were obtained by carefully controlling the amount of water present in the reaction medium and the hydration level of the enzyme macromolecule.

Catalytic conversion of 4-methyl-pentan-2-ol (MPO) was investigated over oxidic materials obtained by the calcination of MgNiCuAl layered double hydroxide (LDH) precursors. Keeping constant the M2+/M3+ ratio equal to 2 (where M2+ = Mg2+, Cu2+, Ni2+ and M3+ = Al3+) various compositions of LDHs were prepared and characterised by X-ray diffraction (XRD), inductively coupled plasma (ICP), N-2 adsorption/desorption and X-ray photoelectron spectra (XPS). The acid-base properties have been investigated by the means of physico-chemical methods such as microcalorimetry, by using ammonia (for acid sites) and carbon dioxide (for base sites) as probe molecules. The conversion of 4-methyl-pentan-2-ol (MPO) was chosen as test reaction to investigate the catalytic activity and selectivity of the oxidic materials obtained by the calcination of MgNiCuAl LDHs and to correlate them with the acid-base properties of the oxide surfaces. Copper was found to increase the alcohol dehydrogenation. (C) 2008 Elsevier B.V. All rights reserved.

In this work a sample of SBA-15 mesoporous silica was synthesized and characterized by TEM, XRD, and N2 adsorption. The sample had a high value of specific surface area (1007 m2 g(-1)) and total pore volume (2.1 cm3 g(-1)). The pore diameter was 67 angstroms, so it was large enough to accommodate protein molecules inside the channels. Immobilization by physical adsorption of a commercial lipase preparation from Mucor javanicus was performed at different pH values (pH 5-8). pH 6 gave the highest lipase loading and hydrolytic activity of the corresponding biocatalyst. Chemical modification of the SBA-15 via glutardialdehyde allowed also the enzyme immobilization through chemical adsorption. This preparation was active toward tributyrin hydrolysis. On the contrary, very low activity toward triolein hydrolysis was observed. The reduction of the size of the channels due the immobilization process has been suggested as a possible explanation.

Three commercial lipases (CLs), A Amano 6 (from Aspergillus niger), M Amano 10 (from Mucor javanicus), and R Amano (from Penicillium roqueforti) – called lipase A, M and R respectively – were characterized in terms of carbohydrate content, protein content and enzymatic activity (p-nitrophenylacetate assay). All the CL preparations contained different proteins as observed from electrophoresis. Lipases were immobilized on Accurel MP1004 porous polypropylene by physical adsorption.The Immobilization process caused a loss of enzymatic activity. The retained activity was similar for lipase M and R (about 15%). In contrast, lipase A retained only the 1.3% of the specific activity of the free lipase. The retained activity of lipases M and R seems to be due to a feature of the support, while the lower activity a of lipase A may be attributed to a strong structure distortion caused by lipase–support interaction.

Oleic acid alkyl esters (biodiesel) were synthesised by biocatalysis in solvent-free conditions. Different commercial immobilised lipases, namely Candida antarctica B, Rizhomucor miehei, and Pseudomonas cepacia, were tested towards the reaction between triolein and butanol to produce butyl oleate. Pseudomonas cepacia lipase resulted to be the most active enzyme reaching 100% of conversion after 6h. Different operative conditions such as reaction temperature, water activity, and reagent stoichiometric ratio were investigated and optimised. These conditions were then used to investigate the effect of linear and branched short chain alcohols. Methanol and 2-butanol were the worst alcohols: the former, probably, due to its low miscibility with the oil and the latter because secondary alcohols usually are less reactive than primary alcohols. Conversely, linear and branched primary alcohols with short alkyl chains (C2–C4) showed high reaction rate and conversion. A mixture of linear and branched short chain alcohols that mimics the residual of ethanol distillation (fusel oil) was successfully used for oleic acid ester synthesis. These compounds are important in biodiesel mixtures since they improve low temperature properties.

Three types of MWW-based catalysts (MCM-22, MCM-36 and ITQ-2) were studied in the liquid-phase alkylation of phenol by tert-butanol (TBA). Ammonia adsorption calorimetry was applied to investigate the acid properties of zeolites with different framework topology and crystallinity. It was established that acid properties of MCM-22 family depend mainly of the solid Al-content (the Si/Al ratio varied from 9.1 to 46.0). Delamination of MCM-22 precursor (MCM-22(P)) leading to ITQ-2 results in the decrease of the total acidity and the increase of the intermediate acid sites concentration, while the pillaring process yielding MCM-36 affected mainly the total concentration of acid sites, the acid strength distribution being similar to the corresponding MCM-22 zeolite. The catalytic activity and selectivity of zeolite-based catalysts are discussed. The most active catalyst for the studied reaction was MCM-22 B (Si/Al similar to 15). The results obtained with MCM-22 as catalyst revealed that, despite the expectations due to the presence of 10-MR pores in the structure of this zeolite, no enhanced selectivity top-tert-butyl phenol (p-TBP) is observed. This has been rationalized by the assumption that most of reactions occurring in this system take place on acid sites at or close to the external surface. This assumption is also supported by the similar catalytic selectivity of the MWW-derived structures (viz. MCM-36 and ITQ-2), which expose a higher concentration of external pockets. However, it is noticeable the high catalytic activity of MCM-22 zeolites for the liquid-phase alkylation of phenol by TBA that is comparable to the gas-phase activity of large pore zeolites like as HY or HM. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.

Dehydrogenation catalysts based on chromia supported on ZrO2, containing about 10wt.% of chromium and increasing amounts of potassium (up to 4wt.%), were prepared and characterised by chemical analysis, N2 adsorption–desorption at 77K, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature programmed reduction (TPR) and adsorption microcalorimetry of ammonia. Increasing K amounts deeply modify the ammonia adsorption behaviour, with a progressive decrease in the acidic features, which are completely lost when the K content attains 1wt.%. Reduction of Cr species seems rather easy for chromia–zirconia and K-containing chromia–zirconia samples with K contents up to 0.5wt.%. The onset of reduction shifts to higher temperatures as the K concentration increases. Catalytic testing was performed under atmospheric pressure at 813K. Pure zirconia is very poorly active in propane dehydrogenation; also virtually inactive are the samples with a K content ≥1wt.%. Conversion decreases as the K amount increases up to 0.5wt.%, propene selectivity being close to 100mol%. An induction period is observed for all the active samples, which attains a maximum in conversion before being deactivated by coking.

The partial oxidation of propane to oxygenates (isopropanol, n-propanol, propionic aldehyde and acetone) is attained in a multifunctional three phase catalytic membrane reactor (3PCMR) operating under mild conditions (T-R, 80-120degreesC; P-R, 140 kPa). A comparative testing of different Nation-based catalytic membranes mediated by Fe2+/H2O2 Fenton system has been carried out. The influences of textural and compositional properties and acid functionality on the catalytic performance of the Nafion membranes are outlined. The enhancing effect of the partial heterogenisation of the Fenton system on reaction rate and H2O2 yield is discussed. (C) 2004 Elsevier B.V. All rights reserved.

The catalytic behaviour of α-Fe2O3-based catalysts in the toluene ammoxidation reaction was investigated in a continuous fixed-bed microreactor at 673K, under atmospheric pressure. Catalysts were prepared and characterized by chemical analysis, N2 adsorption/desorption at 77K, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and adsorption microcalorimetry of ammonia. Differences in the reducibility of the surface sites were found between the pure Fe2O3 and the Na silicate containing catalysts. Doping by addition of V2O5, Sb2O5 or Cr2O3 did not lead to a significant modification of the reduction behaviour. On the contrary, the acidic properties of iron oxide were significantly affected by the presence of both Na silicate and V, Sb or Cr metal oxides. The addition of these minor components resulted in the improvement of the catalytic performance of the pure α-Fe2O3.

The influence of pressure and temperature on the catalytic behaviour of H-beta zeolites in the conversion of sec-butylbenzene, an hydrocarbon present in reformed gasoline, has been investigated. The reaction pathway involves many parallel and/or successive steps, the main reactions being dealkylation, isomerization and disproportionation. The activity and stability of the catalyst increase with increasing pressure. Products distribution is also affected by pressure. An increase in temperature leads to an increase in both conversion and selectivity to dealkylation. The disproportionation and isomerization products are favoured at low temperatures. A general scheme of the process is proposed on the basis of the structural and acidic features of the catalyst. (C) 2002 Elsevier Science B.V. All rights reserved.

Ceria-zirconia catalysts with 100, 75, 50, 25 and 0mol% of ceria have been prepared and characterised by X-ray diffraction, Raman spectroscopy, N2 physisorption, transmission electron microscopy, X-ray photoelectron spectroscopy and adsorption microcalorimetry of probe molecules. All the catalysts have been tested for the conversion of 4-methylpentan-2-ol into 4-methylpent-1-ene, valuable monomer for plastics manufacture. Steady-state 1-alkene selectivity values ranging between 84 and 59% have been observed. The catalytic behaviour has been interpreted on the basis of competing E1cB, E1 and E2 mechanisms, a well balanced concentration of the acid and basic sites with a high strength of the latter being required for optimum performance.

Isomorphously substituted Fe-MFI zeolite catalysts with various Si/Al and/or Si/Fe ratios were synthesized and characterized by many different techniques, such as ICP, XRD, SEM, TPR, microcalorimetry, FTIR, and EPR. Under standard reaction conditions the best catalyst gave 20% benzene conversion and over 90% selectivity to phenol. For Fe-ZSM5 catalysts, addition of steam to the feed improved catalyst activity, selectivity, and durability. Phenol formed onto Fe-based sites only. Active sites could very likely be composed of oxygen-bridged, extraframework binuclear Fe redox species, charge-compensating the framework Fe3+ or Al3+ ions. Surface acidity was not responsible for activity in the main reaction, but it was heavily involved in catalyst deactivation by coking. Catalyst deactivation derived mainly from the decomposition-condensation of phenol onto acid sites; the stronger the latter, the quicker was the coking rate.

A ceria-lanthana system was prepared by the sol-gel technique in order to obtain active catalysts for the 4-methylpentan-2-ol conversion. As the products distribution strongly depends on the acid-base features of the catalyst, acidity and basicity of the CeO2-La2O3 samples were determined by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. Both concentration and strength of the sites were assessed and their nature was investigated by analysing the microcalorimetric data in the light of the structural and textural characterisation previously carried out. Present samples are compared to a formerly investigated ceria-lanthana system prepared by a different procedure.

Wax esters were obtained from lipase-catalysed alcoholysis of triglycerides with cetyl alcohol, using n-hexane as solvent. The heavy triglyceride fraction (HTF), obtained by fractionation of sheep milk fat, was used as raw material. In the natural fat mixture GC analysis showed that palmitic, myristic, stearic and oleic acids are the most abundant fatty acids which are useful to produce wax esters. Reactions were tested for different amounts of Lipozyme RMIM catalyst, and the optimum concentration of 10 mg catalyst/ml solution has been determined. The formation of the four main products, i.e. cetyl myristate, cetyl palmitate, cetyl oleate and cetyl stearate, was determined by HPLC/ELSD quantitative analysis. The optimum water activity in the reaction medium aw=0.35 in the case of Lipozyme RMIM, and aw=0.53 for Novozym 435 was found. Lipozyme RMIM (immobilised sn-1,3-specific lipase from Rhizomucor miehei) was more active than Novozym 435 (immobilised nonspecific lipase-B from Candida antarctica) towards wax esters production. The acyl migration of 2-monoglycerides was suggested as a crucial step to explain the higher yields produced by the 1,3-specific lipase.

In situ FTIR spectroscopy and adsorption microcalorimetry have been employed to study the adsorption/desorption of 2,6-dimethylpyridine (2,6-DMP) on different zirconia and sulfated zirconia (SZ) systems. Adsorption/desorption experiments were carried out at 343 K (beam temperature for all IR experiments) and at 423 K. The adsorbents were (i) a (mainly) monoclinic zirconia, (ii) a crystallographically pure tetragonal zirconia, phase stabilized by formation of a solid solution with 3 mol% Y2O3, (iii) monoclinic sulfated zirconia (m-SZ) and tetragonal sulfated zirconia (t-SZ), both noncalcined and calcined at 923 K, obtained by direct sulfation of the two crystalline ZrO2 specimens, and (iv) two t-SZ specimens (also noncalcined and calcined at 923 K), obtained through the "conventional" sulfation procedure carried out on an amorphous hydroxide precursor and leading, upon thermal treatment at T > 823 K, to crystalline t-SZ. The adsorption/desorption of 2,6-DMP turned out to be a valuable probe for both Bronsted and (to a minor extent) Lewis acidic sites and to yield more information than other bases more frequently adopted (like, for instance, pyridine or ammonia). In particular, for both Bronsted- and Lewis-type interaction, 2,6-DMP is able to distinguish among sites possessing different acidic strength. From the energetic point of view, the process of 2,6-DMP uptake is highly heterogeneous in all systems, and on t-SZ it is dominated by the adsorption of the base in its protonated forms.

The title reaction was investigated over three MOR zeolites with Si/Al ratios of 10, 60 and 80. Surface acidity was evaluated by adsorption microcalorimetry and FTIR analysis, using pyridine as probe molecule. Catalytic tests were carried out at 623K and 40bar in liquid-phase, with decalin as solvent, in a flow reactor. The formation of isopropylnaphthalenes (mainly monoisopropylnaphthalenes) was accompanied by fast oligomerisation/cracking of propene resulting from isopropanol dehydration and trapping of carbonaceous compounds (“coke”) in the zeolite pores. This caused a quasi-immediate blockage of the access to the micropores, suggesting that reactions occur on or near the outer surface of the crystallites. In agreement with this proposal, the activities of the three MOR samples, which have very different acidic properties but similar textural properties, were identical. A reaction scheme involving as a main step transalkylation between naphthalene molecules and the isopropyl aromatic molecules trapped in the MOR channels is proposed to explain the formation of isopropylnaphthalenes over the aged MOR samples. In agreement, isopropylnaphthalenes formation was found to remain significant for more than 1h after substituting a decalin–naphthalene mixture for the normal feed.

Dehydrogenation catalysts based on chromia supported on γ-alumina, containing about 6wt.% of chromium and increasing amounts of potassium (up to 1.8wt.%), were prepared and characterised by means of several techniques, such as N2 adsorption at 77K, X-ray powder diffraction (XRPD), UV-Vis diffuse reflectance spectroscopy (DRS), electron paramagnetic resonance (EPR), temperature programmed reduction (TPR), microcalorimetry and chemical analyses. The catalytic behaviour of the samples was investigated in the propane dehydrogenation reaction at 813K and the effect of potassium loading was examined. The addition of increasing amounts of the alkali metal, as expected, determined a general decrease in the surface acidity. The sites strength distribution was greatly influenced, due to the fact that, at loadings above 0.5wt.%, potassium preferentially caused the disappearance of weak and medium acid sites. EPR showed a decrease of CrIII species (especially α-Cr2O3) on potassium increasing. TPR profiles of the K-containing samples showed the presence of two reduction peaks, ascribable to two different kinds of CrVI surface species with a different reduction behaviour. All catalysts showed a maximum of activity as a function of time-on-stream, due to reduction of CrVI to CrIII species in the first reaction period, and then a decrease, due to deactivation by coking. Propene selectivity was high in all cases and was positively affected by the presence of potassium in concentrations up to 1wt.%.

Candida antarctica lipase B (CALB) and Thermomyces lanuginosa lipase (TLL) were evaluated as catalysts in different reaction media using hydrolysis of tributyrin as model reaction. In o/w emulsions, the enzymes were used in the free form and for use in monophasic organic media, the lipases were adsorbed on porous polypropylene (Accurel EP-100). In monophasic organic media, the highest specific activity of both lipases was obtained in pure tributyrin at a water activity of >0.5 and at an enzyme loading of 10 mg/g support. With tributyrin emulsified in water, the specific activities were 2780 micromol min(-1) mg(-1) for TLL and 535 micromol min(-1) mg(-1) for CALB. Under optimal conditions in pure tributyrin, CALB expressed 49% of the activity in emulsion (264 micromol min(-1) mg(-1)) while TLL expressed only 9.2% (256 micromol min(-1) mg(-1)) of its activity in emulsion. This large decrease is probably due to the structure of TLL, which is a typical lipase with a large lid domain. Conversion between open and closed conformers of TLL involves large internal movements and catalysis probably requires more protein mobility in TLL than in CALB, which does not have a typical lid region. Furthermore, TLL lost more activity than CALB when the water activity was reduced below 0.5, which could be due to further reduction in protein mobility.