Ayyamperumal Sakthivel

para-Selective t-butylation of phenol over mesoporous H-AlMCM-41

Vapour phase alkylation of phenol with t-butyl alcohol (2-methyl-2-propanol) was carried out over mesoporous H-AlMCM-41 in the temperature range 448−498 K. In this reaction, p-t-butyl phenol was obtained as a major product with high selectivity. While the phenol conversion increases with a decrease in phenol-to-t-butyl alcohol ratio, the catalytic activity decreases with time-on-stream due to deactivation of the catalyst. At higher temperatures, both the ortho- and para-isomers, viz., o-t-butyl phenol and p-t-butyl phenol, undergoes isomerization leading to m-t-butyl phenol.

Allylic oxidation of cyclohexene over chromium containing mesoporous molecular sieves

Abstract Allylic oxidation of cyclohexene was carried out over mesoporous (Cr)MCM-41 and (Cr)MCM-48 molecular sieve catalysts. In both the cases, 2-cyclohexen-1-one was obtained as the major product with small amounts of cyclohexene oxide and 1,2-cyclohexandiol. (Cr)MCM-48 showed higher activity than (Cr)MCM-41 owing to the high chromium content in the former. The use of polar solvents such as acetonitrile and methanol decrease the 2-cyclohexen-1-one selectivity; however, such a procedure produces double bond oxidized product, viz. cyclohexene oxide. Furthermore, unlike many other chromium-based solid catalysts, the activity over recycled as well as washed (Cr)MCM-41 and (Cr)MCM-48 remains nearly the same, indicating that the mesoporous chromosilicate materials behave truly as heterogeneous catalysts. In other words, after the initial loss of non-framework chromium ions for the first time, no leaching was noticed for the chromium-based systems.

Tertiary butylation of phenol over mesoporous H–FeMCM-41

Trivalent-iron-substituted mesoporous molecular sieve catalysts (FeMCM-41) were synthesized hydrothermally and characterized systematically by various analytical and spectroscopic techniques. Temperature-programmed desorption studies of ammonia of the protonated catalyst (H–FeMCM-41) indicate a broad distribution of the acid sites. Vapour-phase alkylation of phenol with t-butyl alcohol (2-methyl-2-propanol) was carried out over this solid acid catalyst and p-t-butyl phenol was obtained as the major product with high selectivity.

Novel mesoporous (Cr)MCM-48 molecular sieves: Promising heterogeneous catalysts for selective oxidation reactions

A series of chromium-containing mesoporous MCM-48 molecular sieves, (Cr)MCM-48, with varying Si/Cr (25 − ∝) ratios were synthesized hydrothermally, and characterized systematically by various analytical and spectroscopic techniques. The catalytic performance of the materials was evaluated for the oxidation reactions of certain industrially important organics such as ethylbenzene, cyclohexene and cyclohexane. For all the chosen reactions, the catalyst with a Si/Cr ratio of 50 showed very good conversion and excellent selectivity of the products. Furthermore, (Cr)MCM-48 exhibits much higher activity than the one-dimensional mesoporous (Cr)MCM-41 due to the incorporation of chromium ions in large concentrations as well as to the three-dimensional pore system of the former. Unlike many other chromium-based heterogeneous catalysts, the (Cr)MCM-48 showed only a slight decrease in catalytic activity during first recycling (or second run) experiments, and thereafter it remains nearly the same. Further, the quenching experiments as well as washing studies clearly support the above conclusion. In addition, it can also be deduced from several recycling, washing, filtrate and quenching studies that the leaching of the active chromium ions from the mesoporous matrix is minimal compared to almost all the chromium-based heterogeneous catalysts reported so far. The catalytic activity of (Cr)MCM-48 was also compared with various chromium-containing microporous silicalite-1 and beta, i.e., (Cr)S-1 and (Cr)β, molecular sieves.

Vapour phase tertiary butylation of phenol over sulfated zirconia catalyst

Vapour phase butylation of phenol was carried out over a sulfated zirconia solid superacid catalyst in the temperature range 448–473 K using t-butyl alcohol as the alkylating agent. A good substrate (phenol) conversion and excellent product (para-tertiary BP) selectivity was obtained. The catalytic activity remains nearly the same on repeated use of the catalyst. Further, the catalyst was not deactivated when the reaction was carried out for a longer duration, i.e., even after several hours of reaction.

Influence of aluminium sources on the synthesis and catalytic activity of mesoporous AlMCM-41 molecular sieves

Mesoporous AlMCM-41 molecular sieves were synthesized using various aluminium sources, viz., sodium aluminate, aluminium sulphate, aluminium isopropoxide and pseudoboehmite. The influence of different aluminium sources on the framework substitution of aluminium as well as on the catalytic properties of t-butylation of phenol was studied. Among the aluminium sources, the use of sodium aluminate for the AlMCM-41 synthesis showed maximum incorporation of aluminium in the framework. Further, the catalyst also showed good catalytic activity for the chosen reaction.

Mesoporous (Cr)MCM-41 and (Cr)MCM-48 molecular sieves: promising heterogeneous catalysts for liquid phase oxidation reactions

Chromium-containing mesoporous MCM-41 and MCM-48 silicate molecular sieves were synthesized and characterized. Unlike the chromium-containing microporous materials, the mesoporous analogues show significant activity for the chosen (ethylbenzene oxidation) reaction even after several recycling or washing treatments.

Progress on layered hydrotalcite (HT) materials as potential support and catalytic materials

Mixed metal oxides derived from layered hydrotalcite (HT) materials are extensively used as a potential catalyst and catalytic support in various organic transformations. Numerous such materials have been developed by varying framework divalent and trivalent metal ions, and interlayer anions. The intercalation of anions present in HT facilitates the design of high surface area materials possessing exposed active sites, which enhances the catalytic and adsorption properties. These HT materials have also been used as drug carriers, and in enzyme encapsulation owing to their flexible accommodation of organic anions in the interlayer of the HT structure. The present review is focused on a recent development in the preparation of various HT materials using different metals and intercalating ions and their importance in the various catalytic processes, such as base catalyzed alkylation, isomerization, condensation and esterification. Effectiveness of transition metals containing HT for redox catalytic processes, viz. oxidation of alcohol, alkyl aromatics, phenol and reduction of nitro compounds have been discussed. Further, the importance of the introduction of a hard anion like silicate into the interlayer space of the HT and its applications in various organic reactions has also been covered in this review.

Heterogenisation of CpMo(CO)3Cl on mesoporous materials and its application as olefin epoxidation catalyst

CpMo(CO)(3)Cl reacts with the hydroxyl (Si-OH or Si-OH-Al) functionalities of mesoporous molecular sieves such as MCM-41, MCM-48 and its aluminium analogues during grafting. XRD, N(2) adsorption-desorption, BET surface area analysis and TEM show the resulting samples as being well ordered and maintaining a uniform pore size. FT-IR spectra, elemental analysis, (13)C and (29)Si CP MAS NMR spectra confirm the successful grafting. In the presence of excess TBHP the materials show high activity in cyclooctene epoxidation and good stability.

Vapor-Phase Tertiary Butylation of Phenol Over Mesoporous Gallosilicate Molecular Sieves

Isomorphously substituted GaMCM-41 molecular sieves with different Si:Ga ratio were synthesized and characterized systematically by various analytical and spectroscopic techniques. Temperature-programmed desorption of ammonia was used to identify the nature of acidic sites. For the first time, the vapor-phase tertiary butylation of phenol reaction was carried out over protonated GaMCM-41. The catalysts showed higher (phenol) conversion and good (para-tertiary butyl phenol) selectivity over the Al- and Fe-analogs of MCM-41. Further, the gallosilicates showed good stability both before and after the reaction compared to the aluminosilicates or ferrisilicates.