Al-MCM-41 catalysed alkylation of phenol with methanol (original) (raw)
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Catalytic alkylation of phenol with methanol: factors influencing activities and selectivities
Applied Catalysis, 1990
Six samples of H-ZSM5 zeolites, differing in the size of crystallites and acidity, have been tested as catalysts in the alkylation of phenol with methanol. We observed that the size of crystallites strongly influences activity, even for very small crystallites (220-280 A), by the intervention of intracrystalline diffusion. Kinetic runs have been performed on the most active catalyst. A moderate shape selectivity has been observed only in the formation of p-methylanisole and xylenols. Catalyst deactivation occurs through two mechanisms which are independent of the contact time, the first evolving exponentially and the second linearly. The interpretation of this behaviour and of related consequences on the reaction is discussed in the paper together with the reaction path model. the mechanism and the kinetics.
Journal of Catalysis, 2007
The alkylation of phenol with methanol was studied using a Brønsted-type acid catalyst (a H-mordenite) and basic/dehydrogenating catalysts (MgO, Fe2O3 and Mg/Fe/O), with the aim of investigating the reaction mechanism. The main difference between the two classes of catalysts concerned the transformations occurring on methanol. Specifically, in the former case the acid-type activation of methanol led to the development of an electrophylic species that gave rise to the formation of anisole and of C-alkylated compounds. With basic catalysts, methanol dehydrogenated to formaldehyde, which then underwent transformation to methylformate and to decomposition products, i.e., CO, CO2, CH4 and H2. In this case, the prevailing compounds obtained by reaction with phenol were o-cresol and 2,6-xylenol. The dehydrogenation of methanol was found to be the key-step in the generation of the active methylating species with basic catalysts.
Acetylation of phenol with Al-MCM-41
Catalysis Communications, 2001
Mesoporous Al-MCM-41 molecular sieve materials with three dierent SiO 2 =Al 2 O 3 ratios were used as catalysts for the acetylation of phenol with acetic anhydride and acetic acid as the acetylating agents. The reactions gave 100% ortho-selectivity with acetic acid being the more eective acylating agent. The reactions were run under dierent conditions of temperature, feed¯ow rate, reactant mole ratio and SiO 2 =Al 2 O 3 ratio of the catalyst and all the variables were shown to have signi®cant in¯uence on the acetylation of phenol. A possible reaction mechanism is also suggested. Ó
Selective O-Alkylation of Phenol with Methanol over Sulfates Supported on γ-Al2O3
Journal of Catalysis, 1995
The alkylation of phenol with methanol was studied over La2(HP04)3, BaSO4 and SrS04 catalysts. Studies were conducted in batch liquid phase reactors and in continuous flow reactors. Selectivities for anisole formation were up to 94% over La2(HP04)3 and 907; over BaS04 at 573°K. SrS04 was inactive. In batch liquid phase studies, the high selectivity to anisole was maintained over BaS04 at 86% conversion. La2(HP04)3 showed some decline in selectivity at high conversions. Comparison of these catalysts to A1203, H-ZSM-5 and work reported in the literature is presented. Head,
A cascade mechanism for a simple reaction: The gas-phase methylation of phenol with methanol
Journal of Catalysis, 2019
The gas-phase alkylation of phenol with methanol, a reaction triggered for the production of o-cresol and 2,6-xylenol, is catalysed by MgO-based catalysts. Despite the industrial use of this process, the mechanism of the reaction-which is commonly believed to be based on a classical electrophilic attack of activated methanol onto the aromatic ring-is far from being fully understood. In some previous studies we reported that the reaction intermediate is salicylic alcohol, which is formed by the reaction between the adsorbed phenolate and formaldehyde, the latter being formed in-situ by methanol dehydrogenation. Here we elucidate the following steps of the reaction mechanism, by combining reactivity experiments and DFT calculation, with MgO as a model catalyst. It was found that salicylic alcohol dehydrates into quinone methide, which is then reduced via H-transfer by methanol to o-cresol. Moreover, a dehydrogenation/hydrogenation equilibrium is established between salicylic alcohol and salicylic aldehyde. The methide can also react with methanol to form 2-methoxymethylphenol, which may decompose into ocresol, thus providing an alternative pathway for the formation of the alkylated compound.
Synthesis of cresols by alkylation of phenol with methanol on solid acids
Catalysis Today, 2008
ABSTRACT The gas-phase alkylation of phenol with methanol to obtain cresols was studied at 473 K on SiO2–Al2O3, Al-MCM-41, tungstophosphoric acid (HPA) supported on silica, and zeolites HBEA, HZSM5 and HY. The nature, density and strength of surface acid sites were probed by temperature programmed desorption (TPD) of NH3 coupled with infrared spectra of adsorbed pyridine. Anisole, o-cresol and p-cresol were primary reaction products while m-cresol, xylenols and methylanisoles were secondary products. O- and p-cresols were formed via direct C-alkylation of phenol, and also by conversion of anisole intermediate obtained by O-alkylation of phenol. C-alkylation of phenol was predominant as compared to O-alkylation over all the catalysts, excepting HPA/SiO2. Zeolites HBEA and HY were the most active catalysts for obtaining cresols because both reaction pathways leading from phenol to cresols were particularly promoted by the simultaneous presence of strong Lewis and Bro¨nsted acid sites. However, zeolite HY was rapid and severely deactivated on stream. Phenol methylation was controlled by intracrystalline diffusion on HZSM5 and the narrow channels of this zeolite hindered the formation of bulky intermediates involved in the overalkylation of cresols to xylenols. In contrast, the cresol isomer distribution was practically the same on zeolites HBEA and HZSM5 because HZSM5 did not improve the relative formation of p-cresol by shape selectivity.
Study of Gas Phase m-Cresol Alkylation with Methanol on Solid Acid Catalysts
Catalysis Letters, 2014
The gas-phase alkylation of m-cresol with methanol was studied at 523 K on Al-MCM-41 and zeolites ZnY, HBEA, HZSM5 and HMCM22. The acidity was determined by ammonia TPD and FTIR of adsorbed pyridine. On acid sites of moderate strength (Al-MCM-41), initially the O-alkylation rate was higher than the C-alkylation rate. In contrast, formation of dimethylphenols by C-alkylation was highly favored on ZnY and HMCM22 which have both strong acidity although different nature; Lewis (ZnY) and Brønsted and Lewis (HMCM22). High selectivity of 2,5-DMP was observed on HZSM5, probably due to diffusional constraint. All catalysts, except Al-MCM-41, showed deactivation by coke formation.
Catalytic methylation of phenol on MgO – Surface chemistry and mechanism
Journal of Catalysis, 2010
Reactions of phenol and methanol catalyzed by MgO have been explored by kinetic measurements and in situ IR spectroscopy combined with computational studies of sorbed molecules. On MgO, methanol partly transforms to formaldehyde above 250°C. Adsorbed phenol forms phenolate species, and the energetically preferred mode of adsorption leads to an almost orthogonal orientation of the aromatic ring with respect to the catalyst surface. All molecules involved adsorb preferably at the corner sites of MgO (three-co-ordinated Mg atoms). The main reaction products are anisole and o-cresol, the latter dominating above 300°C. At very low conversions, salicylic aldehyde is observed as primary reaction product, being rapidly transformed to o-cresol. It is only observed during the initial accumulation of adsorbed species on the catalyst surface, but not under steady-state conditions on a fully covered catalyst surface. Therefore, o-cresol formation starts with the reaction between phenol and formaldehyde to salicylic alcohol, which in turn is rapidly transformed to salicylic aldehyde and subsequently to o-cresol. Salicylic aldehyde may also form via the bimolecular disproportionation of salicylic alcohol to o-cresol and aldehyde. The parallel reaction to o-cresol, not involving the formation of salicylic aldehyde as intermediate, proceeds via the reduction of salicylic alcohol to o-cresol by formaldehyde. The identified mechanism may open new synthetic approaches for the production of functionalized phenol derivatives and, even more importantly, for the defunctionalization of substituted phenols potentially available at large scale from deconstructed lignin.
Vapour phase reaction of phenol with ethyl acetate over MCM-41 molecular sieves
Journal of Molecular Catalysis A: Chemical, 2004
The vapour phase reaction of phenol with ethyl acetate was investigated over Al-MCM-41 with Si/Al = 55 and 80, and (Al, Zn)-MCM-41 with Si/(Al + Zn) = 52 at 200, 250, 300, 350 and 400 • C. The products were phenyl acetate (PA), 2-ethylphenol (2-EP), 2-acetylphenol (2-AP) and 4-ethylphenol (4-EP). Phenol conversion increases by increasing temperature up to 350 • C and then decreases at 400 • C. There is no correlation between the acidity and activity of the catalysts. The low activity of (Al, Zn)-MCM-41(52) is due to its high hydrophilicity, which reduces the chemisorption of ethyl acetate on its surface. The low conversion of phenol at low ethyl acetate/phenol feed ratios is attributed to the preferential chemisorption of phenol on the catalyst surface. The decrease in conversion at higher temperature is due to blocking of active sites by coke. This study has revealed that ethyl acetate is an active alkylating reagent for phenol in the vapour phase.