Heterogeneous Acid Catalysis Research Articles

Application of lipase from the physic nut (Jatropha curcas L.) to a new hybrid (enzyme/chemical) hydroesterification process for biodiesel production

The aim of this study was to characterize a new plant enzyme (with high lipase activity) extracted from germinated physic nut seeds, and to apply this lipase to the production of biodiesel using a new process of enzyme/chemical hydroesterification. The lipase activity was detected only in the vegetable enzyme extract from germinated seeds (VEEG). Similar activities were obtained for substrates with different lengths of fatty-acid chains (111 ± 19 U/g for tributyrin (C4:0), 106 ± 49 U/g for tricaprylin (C8:0), and 96 ± 4 U/g for olive oil (C18:1)). The VEEG, obtained by a controlled processes of seed germination, was able to hydrolyze a wide range of biodiesel raw materials (vegetable oils, tallow, and biodiesel waste); of these, soy and physic nut oil showed especially high hydrolysis conversion (97% FFA). The biodiesel (fatty acid methyl esters) was produced by the hydrolysis of the physic nut oil using the VEEG, and subsequent esterification of the generated fatty acids with methanol by heterogeneous acid catalysis (niobic acid in pellets). The resulting biodiesel was of excellent quality, with the following properties: viscosity (5.5 mm2/s), ester content (97.1%), total glycerol (0.09 % w/w), max. methanol (0.05 % w/w), and CFPP (0 °C).

Ethanol transformation over HFAU, HBEA and HMFI zeolites presenting similar Brønsted acidity

Ethanol transformation into higher hydrocarbons in one step by heterogeneous acid catalysis was studied, under 350 °C and 30 bar of total pressure. A comparison was established among three zeolites (HFAU, HBEA and HZSM-5) having the same quantity of Brønsted acid sites but possessing different pore architectures. Large pore HFAU and HBEA zeolites gave mainly increasing yield of ethylene and diethyl ether with time-on-stream, due to the deactivation of the strongest acid sites and only a low quantity of C 3+ hydrocarbons. This was explained by a faster deactivation of large pore zeolites due to fast coke formation which rapidly eliminates strong Brønsted acid sites, required for the transformation of ethylene into higher hydrocarbons. These coke molecules were identified as being polyaromatic compounds. Medium pore zeolite HZSM-5 showed an important formation of C 3+ hydrocarbons (mostly C 5–C 11 compounds) and very small amounts of ethylene and diethyl ether. For this zeolite, after 16 h reaction, there was still complete ethanol transformation into C 3+ hydrocarbons, even though a 55% loss of microporosity and 94% loss of Brønsted acidity were observed. On HZSM-5 the deactivation is slower and the formation of C 3+ hydrocarbons was observed even when the catalyst was saturated with coke molecules (high activity for the hydrogen transfer reactions). It could be possible, that for this zeolite, reaction occurs at the pore mouth of the channel.

Cyclodimerization of α-methylstyrene under homogeneous and heterogeneous acid catalysis conditions

The cyclodimerization of α-methylstyrene in the presence of Bronsted and Lewis acids was realized. The dependence of the cyclic α-methylstyrene dimer yield on the catalyst nature and structure was established. It was shown that the activity of the catalysts is determined by the strength of their acid sites, and the selectivity for the cyclic α-methylstyrene dimer depends on the nature of the anion (homogeneous acids) or the porous structure (heterogeneous catalysts). Sulfuric acid and silicophosphate exhibit the highest selectivity in the cyclodimerization of α-methylstyrene into 1,1,3-trimethyl-3-phenylindane.

ChemInform Abstract: Heterogeneous Lewis Acid Catalysis with Self‐Organized Polymeric Rare Earth Arylsulfonates under Solvent‐Free Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Polarity of the acid chain of esters and transesterification activity of acid catalysts

The effect of polarity of the esters on the transesterification reaction rate has been investigated. The effect was studied in homogeneous and heterogeneous catalysts. The polarity of different ethyl alkanoate esters was varied by (i) increasing the number of carbon atoms in the acid alkyl chain of the esters and (ii) introducing Br and hydroxy substituents at the end of the acid chain of ethyl hexanoate. Polarity was determined through the λ max of the UV–Vis spectrum of the betaine dye dissolved in the investigated esters (E T(30) scale). The transesterification reaction was carried out with methanol and by using sulfuric acid and a Dowex DR2030 sulfonic resin as homogeneous and heterogeneous catalysts, respectively. It was observed that, in addition to steric hindrance, the polarity of the ester chain has an effect on the reaction rate of the heterogeneous acid catalysts. It is proposed that the positive or negative effect of the polarity is due to repulsive or attractive interactions of the ester chain with the polar groups of the resin and/or with the methanol molecules present in the pores. A very positive effect is found in heterogeneous acid catalysis if H-bonds can stabilize the active intermediate participating in the rate determining step. The attractive or repulsive interactions are absent in the homogeneous case.

Heterogeneous Lewis Acid Catalysis with Self-Organized Polymeric Rare Earth Arylsulfonates under Solvent-Free Conditions

Polymeric rare earth arylsulfonates, easily prepared from rare earth triisopropoxides and biphenyl-4,4'-disulfonic acid (BPDSA) or 1,3,5-triphenylbenzene trisulfonic acid (TPTSA) in a self-organization manner, were found to work as an efficient heterogeneous Lewis acid catalyst for the hetero-Diels-Alder reaction of aldehydes with the Danishefsky's diene and the ring-opening reaction of epoxides with amines under solvent-free conditions. The catalysts could be quantitatively recovered and reused many times without decreasing their activities.

Heterogeneous acid catalysis by heteropoly acids: Approaches to catalyst deactivation

Heterogeneous acid catalysis by heteropoly acids (HPAs) has the potential of great economic rewards and green benefits. Its application, however, has been limited to some extent because of a relatively low thermal stability of HPAs, hence difficulty of catalyst regeneration (decoking). The aim of this paper is to discuss approaches to the problem of catalyst deactivation that could be instrumental to achieve sustainable performance of solid HPA catalysts. These approaches include: developing new HPA catalysts possessing high thermal stability, modification of HPA catalysts to enhance coke combustion, inhibition of coke formation on HPA catalysts during operation, reactions in supercritical fluids and cascade reactions using multifunctional HPA catalysis.

Heterogeneous soft acid catalysis of the sucrose hydrolysis

Using a micro-calorimetrical DSC we have compared the acid-catalyzed inversion of sucrose in homogeneous and heterogeneous systems. Acetic acid was chosen as catalyst for homogeneous system, and several carboxylic cationites were used as heterogeneous catalysts. The kinetic apparent parameters (A, E, k ap) for all the systems were calculated from DSC data with Friedmann’s method and catalytic constant, k 323 cat , was further inferred. We found that the specific catalyst efficiency, q cat, in heterogeneous system is over 5000 times higher than in case of homogeneous ones. The activity of heterogeneous carboxylic systems is still about 30 times larger than those of a strong mineral acid in homogeneous catalysis.

ChemInform Abstract: IR Absorption Intensities as a New Spectral Criterion for the Activation of Adsorbed Molecules in Heterogeneous Acid Catalysis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

IR absorption intensities as a new spectral criterion for the activation of adsorbed molecules in heterogeneous acid catalysis

The criterion conventionally used to judge bond activation in molecules adsorbed on active sites of heterogeneous catalysts is the bathochromic shift of the corresponding IR absorption bands. The intensity of these bands, which characterizes bond polariability, can be used as an additional bond activation criterion. This new spectral criterion is particularly promising for acid and acid-base catalysis, in which the activation of adsorbed molecules is due to their polarization by active sites. Examples are provided here to illustrate the fruitfulness of the new approach. These examples include judging the strength of Bronsted acid sites from the intensity of the OH stretching band and an analysis of the dissociative adsorption and dehydrogenation of light paraffins on metal cation forms of zeolites and of proton transfer from Bronsted acid sites to adsorbed paraffin molecules.

Sustainable heterogeneous acid catalysis by heteropoly acids

Heterogeneous acid catalysis by heteropoly acids (HPAs) has the potential of substantial economic and green benefits. Its application, however, has been limited because of the difficulty of catalyst regeneration due to a relatively low thermal stability of HPAs. The aim of this paper is to discuss the perspectives of acid catalysis by solid HPAs, in particular focusing on several approaches that could help overcome the deactivation of HPA catalysts to achieve sustainable catalyst performance. These approaches include: developing novel HPA catalysts possessing high thermal stability, modification of HPA catalysts to enhance coke combustion, inhibition of coke formation on HPA catalysts during operation, reactions in supercritical fluids and cascade reactions using multifunctional HPA catalysis.

A comparison of the esterification of acetic acid with methanol using heterogeneous versus homogeneous acid catalysis

To investigate the similarities and differences between heterogeneous and homogeneous catalyzed esterification, the kinetics of acetic acid esterification with methanol were investigated using a commercial Nafion/silica nanocomposite catalyst (SAC-13) and H 2SO 4, respectively. Reactions were carried out in an isothermal well-mixed batch reactor at 60 °C. Organic base titration, TGA, and elemental sulfur analysis were carried out to estimate the acid site density of SAC-13, permitting the assessment of its catalytic performance for esterification on a per site basis. It was found that SAC-13 has comparable site activity for acetic acid esterification as H 2SO 4. SAC-13 and H 2SO 4 also exhibited similar reaction inhibition due to the presence of water. The similar response to the presence of water and the results of pyridine poisoning experiments suggest that esterification with these catalysts occurs through a common reaction mechanism. Consistent with the hypothesized homogeneous-type reaction mechanism, reaction on SAC-13 appears to involve single-site catalysis with a probable rate-controlling Eley-Rideal surface reaction. A mechanistically derived kinetic model successfully predicts the esterification rate of SAC-13 as reaction progresses. The dissimilarities between homogeneous and heterogeneous acid-catalyzed esterification are also discussed.

New Perspective in Recent Solid Acid Catalyst

This paper will review on the latest development on solid acid catalysts used in industries as well in research activities. Application of heterogeneous acid catalysis becomes current trend for many industries due to world wide environmental concern. Conventional synthetic or natural zeolites widely used for petrochemical processing, has some limitation because its pore size is normally smaller than reactant molecules. To overcome this challenge new delaminated zeolite process was introduced. In this process specific synthetic zeolite (i.e. ferrierite) was swelled up using specific surfactant followed by sonification to produce the delaminated zeolite. Further modification of this material such as sulfonification reaction to its surface has been found to improve the catalytic activity and selectivity for esterification reaction. Other acid catalyst systems based on mesoporous molecular sieves and Keggin heteropolyacids (HPA) are also discussed in this paper.

Alkane C−H Bond Activation in Zeolites: Evidence for Direct Protium Exchange

The mechanism of alkane C-H bond activation in heterogeneous acid catalysis is unknown. (1)H solid-state NMR techniques have been used to simultaneously detect the reactivity of both catalyst and alkane reactant protons in a true in-situ experimental design. Specifically, the activation of isobutane C-H bonds by the solid acid zeolite HZSM-5 is directly observed, and the rate of proton transfer between the solid catalyst surface and gaseous isobutane is quantitatively measured using isotopic (1)H/(2)H exchange methods. An observable adsorption complex forms between the isobutane and the primary Bronsted acid site of ZSM-5, which leads to proton exchange between the zeolite surface and the isobutane methyl groups at temperatures (273 K) much lower than previously reported. The secondary acid site in ZSM-5 is less accessible to or less reactive with the isobutane molecule. Simultaneous detection of protium loss from the Bronsted acid site and protium gain by perdeuterated isobutane reveals a common rate constant equal to 4.1-4.6 x 10(-4) s(-1) at 298 K, but at lower temperatures, the transition between this and a much slower rate process is resolved. The measured activation energy for isobutane H/D exchange is 57 kJ/mol. In all experiments, the isobutane reagent was purified to eliminate any unsaturated impurities that might serve as initiators for carbenium-ion mechanisms, and the active catalyst was free of any organic contaminants that might serve as a source of unsaturated initiators. In total, our results are consistent with direct proton exchange between the zeolite surface and the methyl groups of isobutane.

Transformations of Isocaryophyllene Diepoxide under Conditions of Homogeneous and Heterogeneous Acid Catalysis

Transformations of isocaryophyllene diepoxide (an isomer of widely spread natural sesquiterpene) were studied in various acidic media under conditions of homogeneous and heterogeneous catalysis. A number of previously unknown compounds were thus obtained. The experimental data were compared with the results of molecular-mechanics and quantum-chemical simulation of the most probable transformation paths.

Synthesis of 2‐Alkylbenzofurans via Acid‐Catalyzed Cyclization of 1,1‐Dimethoxy‐2‐phenoxyalkanes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Nanostructured, Scandium-Containing Polymer for Heterogeneous Lewis Acid Catalysis in Water

A nanostructured, polymer-supported Sc(III) catalyst for heterogeneous Lewis acid catalysis in water was prepared by quantitative Sc(III) exchange of a cross-linked inverted hexagonal assembly containing sodium sulfonate groups. The material was found to catalyze Mukaiyama aldol and Mannich reactions with a syn/anti product ratio of ca. 2/1, whereas Sc(III) catalysts in solution and on amorphous polymer supports do not show any significant syn/anti diastereoselectivity under similar conditions.

Furfuryl alcohol conjugated oligomer pellicle formation

The heterogeneous acid catalysis of furfurylic alcohol oligomer polymerisation was investigated for the first time. Oligomer conjugated bond structures were confirmed through their optical absorption bands at 570, 650, 770 and 930 nm. Polymerisation in the furfurylic alcohol surface inside glass tubes produced porous pellicles that fell as a result of gravity, breaking apart when tube radii were larger than 0.27 cm. The high oligomer concentration at the furfurylic alcohol surface caused the formation of oligomer clusters that bound to each other to generate the porous and electrically conductive pellicle. Oligomers produced by heterogeneous catalysis have a molecular weight distribution richer in small oligomers than those produced by homogeneous catalysis.

Activity–acidity relationship in zeolite ZSM-5. Application of Brönsted-type equations

In this paper the relation between activity and acidity in a variety of ZSM-5 zeolite catalysts, with different Si/Al ratios and different protonic content, is analysed and a quantitative correlation is obtained. The acid site strength distribution was estimated using temperature-programmed desorption (TPD) of ammonia by applying a digital deconvolution method to the curves. These data were then correlated with experimental catalytic activity data for the same catalysts towards n-heptane cracking reaction, by means of a Brönsted-type equation similar to the ones used for homogeneous acid catalysis and already used for other zeolites. It can be noticed that the same types of equation that are used for homogeneous acid catalysis also hold for heterogeneous acid catalysis and that the activation energy for ammonia desorption can be used as acid-strength scale for the purpose of correlation with catalytic activity.

The role of acidity in the catalytic hydroxylation of phenol by hydrogen peroxide

The heterogeneous acid catalysis of the hydroxylation of phenol by hydrogen peroxide was investigated over protonic faujasites containing various amounts of aluminium or partially neutralized. Over strong acids, such as dealuminated protonic faujasites, dihydroxybenzenes result, mainly from an acid catalysed electrophilic aromatic substitution. Over weaker acids, an induction period is observed, the length of which is related to the strength of the acid sites. In that case, the initiation of the reaction occurs by the products of the former acid mechanism, and it is demonstrated using protonated and unprotonated electron transfer agents, that the subsequent autocatalysis involving a redox mechanism, also needs acid catalysis.