S. Sugunan

Surface properties and catalytic activity of ferrospinels of nickel, cobalt and copper, prepared by soft chemical methods

Abstract Ferrospinels of nickel, cobalt and copper and their sulphated analogues were prepared by the room temperature coprecipitation route to yield samples with high surface areas. The intrinsic acidity among the ferrites was found to decrease in the order: cobalt>nickel>copper. Sulphation caused an increase in the number of weak and medium strong acid sites, whereas the strong acid sites were left unaffected. Electron donor studies revealed that copper ferrite has both the highest proportion of strong sites and the lowest proportion of weak basic sites. All the ferrite samples proved to be good catalysts for the benzoylation of toluene with benzoyl chloride, copper and cobalt ferrites being much more active than nickel ferrite. The catalytic activity for benzoylation was not much influenced by sulphation, but it increased remarkably with calcination temperature of the catalyst. Surface Lewis acid sites, provided by the octahedral cations on the spinel surface, are suggested to be responsible for the catalytic activity for the benzoylation reaction.

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

Abstract 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.

Study of cyclohexanol decomposition reaction over the ferrospinels, A1−xCuxFe2O4 (A=Ni or Co and x=0, 0.3, 0.5, 0.7 and 1), prepared by ‘soft’ chemical methods

Preparation of simple and mixed ferrospinels of nickel, cobalt and copper and their sulphated analogues by the room temperature coprecipitation method yielded fine particles with high surface areas. Study of the vapour phase decomposition of cyclohexanol at 300 ◦ C over all the ferrospinel systems showed very good conversions yielding cyclohexene by dehydration and/or cyclohexanone by dehydrogenation, as the major products. Sulphation very much enhanced the dehydration activity over all the samples. A good correlation was obtained between the dehydration activities of the simple ferrites and their weak plus medium strength acidities (usually of the Brnsted type) determined independently by the n-butylamine adsorption and ammonia-TPD methods. Mixed ferrites containing copper showed a general decrease in acidities and a drastic decrease in dehydration activities. There was no general correlation between the basicity parameters obtained by electron donor studies and the ratio of dehydrogenation to dehydration activities. There was a leap in the dehydrogenation activities in the case of all the ferrospinel samples containing copper. Along with the basic properties, the redox properties of copper ion have been invoked to account for this added activity.

A comparison on the catalytic activity of Zn1−xCoxFe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0)-type ferrospinels prepared via. a low temperature route for the alkylation of aniline and phenol using methanol as the alkylating agent

Depending on the variation of the Zn2+/Co2+ ratio in the Zn1−xCoxFe2O4 (x=0, 0.2, 0.5, 0.8 and 1.0)-type ferrospinels, the systems showed different activity trends for aniline and phenol methylation using methanol as the alkylating agent. An increase in Zn2+/Co2+ ratio increased the rate of N-monomethylation of aniline, whereas, a decrease in the ratio favored the rate of ortho methylation of phenol. An attempt has been made to interpret the observed trends based on the variation of surface acid–base properties of the catalyst surface with changes in the spinel composition. The efficiency of adsorption of aniline, phenol or methanol depends not only on the catalyst surface acid–base properties but also on the polarity of the adsorbing molecules. A controlled interplay of surface acid–base properties and polarity of the respective reacting molecules determines the efficiency of a particular reaction. In the case of aniline methylation, surface basicity plays a dominating role, whereas for phenol methylation surface acidity plays a dominating role.

Selective benzoylation of o-xylene to 3,4-dimethylbenzophenone using various zeolite catalysts

Abstract The liquid phase benzoylation of o -xylene with benzoyl chloride (BOC) over various zeolite catalysts is studied in a batch reactor at atmospheric pressure and 411 K. The results obtained over different zeolite catalysts are compared with the homogeneous Lewis acid catalyst, AlCl 3 and amorphous silica–alumina. The protonic form of zeolite beta is found to be an efficient catalyst compared to other zeolites in the benzoylation of o -xylene. The conversion of BOC, turnover rate of BOC conversion (TOF) and selectivity for 3,4-dimethylbenzophenone (3,4-DMBP) over zeolite H-beta are found to be 52.8 wt.%, 69.7×10 −5 s −1 mol −1 Al and 94.7 wt.%, respectively, at the following reaction conditions [H-beta to BOC (w/w)=0.28, o -xylene to BOC (molar ratio)=5; 411 K; 1 atm]. The non-shape selective AlCl 3 catalyst produces higher amount of consecutive products (16.2 wt.%) and hence gives lower selectivity for 3,4-DMBP (76.5 wt.%). The acidity and pore structure of H-beta appeared to be responsible for good performance. Increase in reaction time, catalyst concentration, reaction temperature, o -xylene to BOC molar ratio enhances the conversion of BOC, whereas it decreases with the increase in degree of Na-exchange and SiO 2 /Al 2 O 3 molar ratios of H-beta. The zeolite H-beta is recycled three times without the loss of 3,4-DMBP selectivity but with a decline in the catalytic activity of H-beta. Additionally, the benzoylation of m -xylene and p -xylene is also investigated using H-beta. The Friedel–Crafts acylation reaction mechanism involves the formation of an electrophile (C 6 H 5 CO + ) over an acidic zeolite catalyst which attacks the xylene ring resulting in the formation of dimethyl benzophenones.

A comparative study on aniline alkylation activity using methanol and dimethyl carbonate as the alkylating agents over Zn-Co-Fe ternary spinel systems

The catalyst compositions of the Zn1 x Cox Fe2O4 (xD 0, 0.2, 0.5, 0.8 and 1.0) spiel series possessing ‘ x’ values, x0.5, are unique for selective N-monomethylation of aniline using methanol as the alkylating agent. Since dimethyl carbonate (DMC) is another potential non-toxic alkylating agent, alkylation of aniline was investigated over various Zn‐Co ferrites using DMC as the alkylating agent. The merits and demerits of the two alkylating agents are compared. Catalytic activity followed a similar trend with respect to the composition of the ferrospinel systems. DMC is active 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 gave appreciable amounts of N,N-dimethylaniline (NNDMA) even at low temperature where methanol gave nearly 99% N-methylaniline (NMA) selectivity. As in the case of methanol, DMC also did not give any C-alkylated products.

Photoacoustic study of the effect of degassing temperature on thermal diffusivity of hydroxyl loaded alumina

The thermal diffusivity of γ‐alumina is determined by the photoacoustic method. The method is calibrated by determining the thermal diffusivity of copper and aluminum. The effect of the chemisorbed hydroxyl groups on thermal diffusivity is studied by degassing the sample at different temperatures.

Evanescent wave fibre optic sensors for trace analysis of Fe3+ in water

In this communication, we discuss the details of fabricating an off-line fibre optic sensor (FOS) based on evanescent wave absorption for detecting trace amounts of Fe3+ in water. Two types of FOS are developed; one type uses the unclad portion of a multimode silica fibre as the sensing region whereas the other employs the microbent portion of a multimode plastic fibre as the sensing region. Sensing is performed by measuring the absorption of the evanescent wave in a reagent medium surrounding the sensing region. To evaluate the relative merits of the two types of FOS in Fe3+ sensing, a comparative study of the sensors is made, which reveals the superiority of the latter in many respects, such as smaller sensing length, use of a double detection scheme (for detecting both core and cladding modes) and higher sensitivity of cladding mode detection at an intermediate range of concentration along with the added advantage that plastic fibres are inexpensive. A detection limit of 1 ppb is observed in both types of fibre and the range of detection can be as large as 1 ppb–50 ppm. All the measurements are carried out using a LabVIEW set-up.

Selective N-methylation of aniline with dimethyl carbonate over Zn1−xCoxFe2O4 (x=0, 0.2, 0.5, 0.8 and 1.0) 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-monomethylation of aniline over Zn1−xNixFe2O4 (x=0, 0.2, 0.5, 0.8 and 1) type systems

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.