The alkylation of phenol with methanol is conducted over Ni 1− x Co x Fe 2 O 4 ( x =0, 0.2, 0.5, 0.8 and 1.0) type systems prepared via low temperature route. Alkylation leads to predominantly ortho methylation of phenol, yielding o -cresol and 2,6-xylenol as the products. Under optimized conditions, the total ortho selectivity was ≥94%, regardless of the catalyst composition. Only traces of anisole is formed and hardly any other xylenol or cresol isomers are detected. Phenol conversion and the individual selectivities for o -cresol and 2,6-xylenol depend strongly on the catalyst composition. Selectivity for o -cresol was maximum for NiFe 2 O 4 (i.e., when x =0), whereas upon progressive substitution of Co 2+ ions for Ni 2+ ions, the 2,6-xylenol selectivity increases with a concomitant decrease in the o -cresol selectivity. Maximum phenol conversion and 2,6-xylenol selectivity (also total ortho selectivity) were observed over CoFe 2 O 4 ( x =1). The activity and selectivity were shown to be strongly dependent on the surface acid–base properties of the system. The influences of surface acidity, cation distribution in the spinel lattice and various reaction parameters are discussed.

Ferrospinels based on Co and Ni prepared via a low temperature route as efficient catalysts for the selective synthesis of o-cresol and 2,6-xylenol from phenol and methanol

Palladium nanoparticles supported on CNT functionalized by rare-earth oxides for solvent-free aerobic oxidation of benzyl alcohol

A series of Ni–Co ferrites with the general formula Ni1-x
Co
 x
 Fe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0) was prepared by a low-temperature hydroxide coprecipitation route. The catalyst systems were characterized by adopting various physico-chemical techniques. Alkylation of pyridine with methanol was carried out in a down-flow vapor-phase reactor. The influence of surface acid–base properties, cation distribution in the spinel lattice and various reaction parameters are discussed. It was observed that the systems possessing x values ≥0.5 are selective for 3-picoline formation, whereas the ones with x values 0 and 0.2 give a mixture of 2- and 3-picolines. Pyridine conversion increased with the progressive substitution of Ni2+ ions by Co2+ ions. Cation distribution in the spinel lattice influences their acidic and basic properties, and these factors have been adequately considered as helpful to evaluate the activity of the systems.

Selective synthesis of 3-picoline via the vapor-phase methylation of pyridine with methanol over Ni1-xCoxFe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0) type ferrites

The reaction of aniline with methanol was carried out over Zn1−xNixFe2O4 (x=0, 0.2, 0.5, 0.8 and 1) type systems in a fixed-bed down-flow reactor. It was observed that systems possessing low “x” values are highly selective and active for mono N-alkylation of aniline leading to N-methyl aniline. Selectivity for N-methyl aniline over ZnFe2O4 was more than 99% under the optimized reaction conditions. Even at methanol to aniline molar ratio of 2, the yield of N-methyl aniline was nearly 55.5%, whereas its yield exceeded 67% at the molar ratio of 7. The Lewis acid sites of the catalysts are mainly responsible for the good catalytic performance. Cation distribution in the spinel lattice influences their acido-basic properties, and hence, these factors have been considered as helpful to evaluate the activity and stability of the systems.

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Selective N-monomethylation of aniline over Zn1-xNixFe2O4 (x=0, 0.2, 0.5, 0.8 and 1) type systems

The alkylation of aniline with dimethyl carbonate (DMC) is reported over Zn1−xCoxFe2O4 (x=0, 0.2, 0.5, 0.8 and 1.0) type systems prepared via. coprecipitation route. The influence of surface acid–base properties, cation distribution in the spinel lattice and various reaction parameters are discussed. It was observed that systems possessing low x values are highly selective and active for N-alkylation leading to N-methyl aniline as the major product. Since the authors have already reported the alkylation reaction using methanol as the alkylating agent over the same ferrospinel systems, in some cases both data are compared to highlight the merits and demerits of the choice of the two alkylating agents. DMC is acting as a better alkylating agent at comparatively low temperature, where methanol shows only mild activity. However, on the selectivity basis DMC as an alkylating agent could not compete with methanol, since the former executed appreciable amount of N,N-dimethylaniline (NNDMA) even at low temperature where methanol gave nearly 99% NMA selectivity. Cation distribution in the spinel lattice influences its acido-basic properties, and hence, these factors have been considered as helpful to evaluate the activity and stability of the systems.

Selective N-methylation of aniline with dimethyl carbonate over Zn1−xCoxFe2O4 (x=0, 0.2, 0.5, 0.8 and 1.0) type systems

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G. Devikarani

Papers

Electron donor sites on Y2O3 catalyst as a function of the activation temperature