J. Vital

Effect of extra-lattice aluminium species on the activity, selectivity and stability of acid zeolites in the liquid phase isomerisation of α-pinene

Abstract The liquid phase isomerisation of α-pinene was studied on a number of zeolite catalysts at 150°C. The primary reaction products were camphene, tricyclene and p -menthadienes. Catalyst samples with lattice Si/Al ratios ranging from 1.46 to ca. 200 were prepared by hydrothermal treatment of zeolites Y and X. The nature of extra-framework aluminium species was investigated by 27 Al-MAS-NMR spectroscopy. For high values of N Al (number of framework aluminium atoms per unit cell) extra-lattice aluminium (EFAL) species have a promoting effect on the catalytic activity. On the other hand, for the highly dealuminated samples the catalytic activity decreases with N Al . However it does not seem to become zero for zero Bronsted acidity, suggesting that Lewis acid sites are also active on α-pinene isomerisation. Selectivity towards camphene is also strongly affected by EFAL species, decreasing at high values of N Al and increasing for the catalyst samples with high EFAL content. The different distribution of EFAL species in the catalysts prepared at different temperatures would cause this effect on selectivity.

Activated carbons with immobilised manganese(III)salen complexes as heterogeneous catalysts in the epoxidation of olefins: influence of support and ligand functionalisation on selectivity and reusability

A manganese(III) N2O2 Schiff base complex functionalised with hydroxyl groups on the aldehyde moieties, [Mn(4-HOsalhd)CH3COO], was immobilised onto a commercial activated carbon and on its air and acid oxidised forms: the unfunctionalised manganese(III) salen complex [Mn(salhd)Cl] was also immobilised onto the air oxidised activated carbon. All the materials were characterised by elemental analyses and by XPS and the type of oxygen functionalities present at the surface of the various activated carbons was characterised by TPD. The catalytic activities in the epoxidation of styrene of the manganese(III) salen complexes in homogeneous phase and heterogenised onto the activated carbon based materials were studied, using iodosylbenzene as oxidant and acetonitrile as solvent. All the heterogeneous catalysts are as chemoselective towards the styrene epoxide as their homogeneous counterparts, with the exception of the complex supported onto the nitric acid oxidised activated carbon, which exhibited the lowest values, a consequence of the catalytic role of the support. Catalyst reutilisation studies showed that the hydroxyl functionalised manganese(III) complex supported onto the two oxidised activated carbons kept the catalytic activity, contrasting with the hydroxyl functionalised manganese(III) complex supported onto the untreated activated carbon and the unfunctionalised manganese(III) complex supported onto the air oxidised activated carbon, for which a decrease in styrene epoxide yield was clearly observed. These results indicate that lack of oxygen functionality on the activated carbon or of complex functionalisation results in the deactivation of the manganese(III) salen based heterogeneous catalyst as a consequence of inefficient active phase anchoring. Conversely, the combination of support oxidation and of suitable complex functionalisation leads to the establishment of a covalent attachment of the hydroxyl functionalised Mn(III) complexes onto the carbon surface oxygen groups that retains an efficient site isolation of the complexes, both needed to produce very stable and reusable catalysts.

Hydration of α-pinene over zeolites and activated carbons dispersed in polymeric membranes

Abstract The acid catalysed hydration of α-pinene yields a complex mixture of monoterpenes, alcohols and hydrocarbons. By controlling the reaction variables is possible to make it selective to the terpenic alcohols, namely α-terpineol. In this paper the results of the hydration reaction of α-pinene catalysed by polydimethylsiloxane (PDMS) membranes filled with zeolite USY, zeolite beta or a surface modified activated carbon, are reported. The reaction is carried out at 50°C, using aqueous acetone as solvent. The activity and selectivity towards α-terpineol of the composite membranes are compared with those of the free catalysts.

The acid-catalysed reaction of α-pinene over molybdophosphoric acid immobilised in dense polymeric membranes

Abstract The α-pinene hydration to α-terpineol was studied using as catalysts polymeric catalytic membranes consisting of HPMo entrapped in polyvinyl alcohol (PVA) cross-linked with 10, 20 and 30% of succinic acid, and HPMo encaged in USY zeolites dispersed in a polydimethylsiloxane (PDMS) matrix. In the case of HPMo/PVA membranes it was observed that membrane activity increases with the polymer cross-linking, due to the increase in membrane hydrophobicity, up to the limit of the increasingly restrictions to the molecules mobility. The HPMo-USY/PDMS membrane shows a significantly higher activity for pinene hydration, which is even higher than that observed with USY encaged HPMo alone. However, selectivity to α-terpineol (65% at 80% conversion) is slightly lower than that obtained for the HPMo/PVA cross-linked with 20 or 30% of succinic acid (70–75% at 90% conversion). For both catalytic membranes, HPMo/PVA or HPMo-USY/PDMS, the stability is reasonable good and catalyst activity increases in the subsequent uses of the same membrane, probably due to the interaction between retained α-terpineol and the polymer matrix.

The effect of α-terpineol on the hydration of α-pinene over zeolites dispersed in polymeric membranes

Abstract The hydration of α-pinene over catalytic PDMS membranes loaded with a USY zeolite is studied. The concentration profiles of reagent and products exhibited a pronounced initial induction period followed by a rapid increase of the reaction rate, suggesting an autocatalytic behaviour. The effects of the main reaction product, α-terpineol, on the membrane transport properties are investigated. A simple diffusion-kinetic model which fits experimental concentration data quite well has been developed.

Vanadium as a catalyst for NO, N2O and CO2 reaction with activated carbon

The kinetics of the reaction of NO, N 2 O and CO 2 with activated carbon without catalyst and impregnated with a precursor salt of vanadium (ammonium monovanadate) was investigated. The conversion of NO, N 2 O and CO 2 was studied (450-900°C) using a TGA apparatus and a fixed bed reactor. The reactor effluents were analysed using a GC/MS on line. The addition of vanadium increased carbon reactivity and adsorption at lower temperatures. For NO and N 2 O conversion the main products obtained were N 2 , N 2 O, CO and CO 2 but for CO 2 conversion only CO was detected. In situ XRD was a useful tool for interpreting catalyst behaviour and identifying phases present during reaction conditions. The catalytic effect of vanadium can be explained by the occurrence of redox processes in which the catalyst is reduced to lower oxidation states such as V 2 O 5 /V 6 O 13 .

Oxidation of pinane using transition metal acetylacetonate complexes immobilised on modified activated carbon

The performance of a new solid catalyst is studied. Copper and cobalt acetylacetonate complexes are chemically anchored to functionalised activated carbon. These catalysts are active and highly selective to 2-pinane hydroperoxide in the oxidation of pinane at room temperature and atmospheric pressure.

Hydrolysis of sucrose using sulfonated poly(vinyl alcohol) as catalyst.

The hydrolysis of sucrose was carried out over poly(vinyl alcohol) (PVA) with sulfonic acid groups, at 80 degrees C. The products of sucrose hydrolysis were glucose and fructose. A series of PVA with different crosslinking degree were prepared. It was observed that the catalytic activity of PVA matrix increases with the crosslinking degree, due to the increases of the amount of sulfonic acid groups on PVA. Further, the influence of various reaction parameters, such as, catalyst loading, initial concentration of sucrose and temperature, on the hydrolysis of sucrose over PVA_40 was studied. It was found that at 80 degrees C, with 0.511 g of catalyst loading and with an initial concentration of sucrose of 0.6M, a sucrose conversion of about 90%, after 3h, could be obtained. The PVA_40 catalyst was recycled and reused with negligible loss in the activity. A simple kinetic model was developed assuming that the sucrose hydrolysis is an irreversible reaction and the first order with respect to the sucrose concentration. Since the concentration profiles of the reactant and the products do not exhibit any pronounced initial inductive period, the external and internal diffusion of the reactant and products on the catalyst were not considered. It was observed that the kinetic model fits experimental concentration data quite well.

OXYDEHYDROGENATION OF CYCLOHEXANOL OVER CARBON CATALYSTS

Abstract The reaction of cyclohexanol over carbon catalysts with surfaces of different chemical nature was studied. The catalyst samples were prepared by treating a parent activated carbon with HNO3, H2O2, O2 and N2O. The catalytic tests were performed in a packed-bed reactor at 350 °C. Dehydration as well as dehydrogenation of the substrate occur under the reaction conditions. The main products obtained are cyclohexene, cyclohexanone, benzene and phenol. Dehydration occurs preferentially over the carbon treated with HNO3, while the best selectivity to cyclohexanone is achieved with the carbon treated with H2O2. The catalyst sample treated with N2O is highly selective to phenol. A mechanism involving nitro groups on the carbons surface is proposed.

Oxidation of pinane to 2-pinane hydroperoxide over encaged metal phthalocyanines in Y zeolites. Mechanism and kinetic modelling

Abstract The influence of the oxygen donor (t-butyl hydroperoxide [t-BHP], O2, H2O2) and the central metal (Cu, Co, Fe, Mn), on the activity and selectivity of metallophthalocyanines when free or encaged in NaY, for the oxidation of cis-pinane, is reported. The effect of encapsulation enhances catalyst stability and influences its activity and selectivity. Encaged complexes yield mainly 2-pinane hydroperoxide and insignificant amounts of 2-pinanol, while with their homogeneous counterparts, selectivities to 2-pinanol are higher. The ratio of 2-pinane hydroperoxide/2-pinanol depends on the amount of the complex, indicating that 2-pinane hydroperoxide is also in this last case, the primary oxidation product. With the purpose of checking the effect of the concentration of the oxidant agent on selectivity, oxidation experiments were carried out with slow addition of t-BHP, under semibatch conditions. A chain reaction mechanism initiated by t-BHP decomposition is proposed and a kinetic model was built for the semibatch reactor assuming internal mass transfer limitations concerning pinane.