Puyam S. Singh

Vapour phase beckmann rearrangement of cyclohexanone oxime over SAPO-11 molecular sieve

Abstract SAPO-11 exhibited a high caprolactam yield for the vapour phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. At 663 K, the oxime conversion is 99,9% with a caprolactam selectivity around 85.7%. The effect of silicon content of the SAPO-11 on the catalytic efficiency is compared with aluminosilicate having MFI structure. SAPO-11 is the best catalyst for the reaction among the investigated catalysts, ALPO 4 -11 on silica carrier, silynated zeolite and silynated SAPO-11. Acid sites with medium strength ( Si / Al > 10 000) are very active in the rearrangement reaction.

Transalkylation of cumene with toluene over zeolite Beta

The transalkylation of cumene with toluene over zeolite H-Beta is described. The influence of various reaction parameters on the cymene selectivity and cumene conversion are discussed. The optimum conditions for the selective transalkylation are found to be temperature 473–493 K, WHSV 4.2 h−1 and toluene-to-cumene molar ratio 14. The catalytic activity is compared with that of H-Y and H-ZSM-12 zeolites. Lower activities over these catalysts are attributed to their acidic and structural properties. Decrease in total activity with increase in the p-cymene formation is observed with time on stream in these catalysts due to coke induced shape selectivity and inhibition in the secondary isomerization process.

Aniline methylation over AEL type molecular sieves

Abstract ALPO-11, SAPO-11 and MAPSO-11 were prepared hydrothermally. These microporous solid catalysts could be used for the synthesis of industrially important N -alkylated products during aniline methylation. The activity of these catalysts was compared with aluminosilicates of high silica having MFI structure. A number of stronger acid sites enhance successive alkylation. Activity and selectivity of N , N -dialkylated product for SAPO-11 is higher at all temperatures as compared to that of ALPO-11. By introduction of Mg in SAPO-11, during hydrothermal synthesis, a decrease in total acid strength and an increase in basic strength, as compared to SAPO-11, is observed. This acidity-basicity function is correlated with the activity of the catalyst and product pattern of the methylation of aniline. C -alkylated products via direct alkylation of aniline with methanol are not enhanced during the alkylation reaction, catalysed by ALPO-11 and its derivatives, whereas the reaction catalysed by aluminosilicates and high silica aluminosilicates with MFI structure, some amount of C -alkylated products (toluidines) are formed.

Characterization of SAPO-11 synthesized conventionally and in the presence of fluoride ions

SAPO-11 samples have been synthesized by the conventional route and from an aqueous solution containing F– anions. Characterization of these samples by X-ray diffraction (XRD), chemical analysis, X-ray photoelectron spectroscopy (XPS), thermal analysis, NMR, adsorption measurements and catalytic test reaction reveals that the samples are highly crystalline, but differ in some physico-chemical properties. These differences in the properties of SAPO-11 obtained via different synthesis routes are correlated with different ordering of silicon substitution within the framework.

Selective acidic, oxidative and reductive reactions over ALPO-11 and Si or metal substituted ALPO-11

Publisher Summary Aluminophosphate molecular sieves are microporous crystalline inorganic solids. ALPO-11 and derivatives of ALPO-11 containing Si, V, Co, Mn have been synthesized using n-dipropyl amine as a template. The addition of these elements in ALPO-11 considerably influences the physical and catalytic properties of the materials synthesized, due to the generation of new catalytic centers. The samples were characterized by XRD, SEM, ESR, UV-Visible and sorption measurements. The acidic characteristics of the samples were evaluated in the hydrocarbon reactions, like toluene methylation, m-xylene isomerization, and isobutanol dehydration. The product pattern obtained in the methylation of toluene and isomerisation of m-xylene with Si or metal-substituted ALPO-11 is similar to that obtained for zeolites. For these two reactions, ALPO-11 did not show any catalytic activity. The studies distinguish two types of acid centers in ALPO-11 and SAPO-11. ALPO-11 being, very weakly acidic due to terminal hydroxyl group or weak Lewis acid sites, is not having catalytically active centers for alkylation and isomerisation, but is active for the isobutanol dehydration. Further studies indicate that metal-substituted ALPO-11 generates additional few stronger acid centers due to the substitution of M 2+ in place of A 13+ in the AEL structure. These acid centers are stronger than the acid centers of SAPO-11; however, acidity of these molecular sieves is much weaker as compared to that of a zeolite. Metal substituted ALPOs also exhibit activity in the hydrogenation of nitrobenzene and oxidation of benzyl alcohol, thus, demonstrating the reductive and oxidative properties, due to the introduction of new metallic sites.

Spectroscopic studies of vanadium incorporated SAPO-11

Abstract The incorporation of vanadium during the hydrothermal synthesis of SAPO-11 is reported. The sample is characterized by different spectroscopic techniques namely XRD, ESR, TPR, UV-VIS and 51 V MAS-NMR. ESR, UV-VIS and 51 V MAS-NMR studies reveal that vanadium in VAPSO-11 is located in square pyramidal or distorted octahedral structures. Vanadium shows redox behaviour (V 4+ to V 5+ and vice versa) when calcined and reduced. Samples prepared by impregnation of vanadium into SAPO-11 (V-SAPO-11) are compared with VAPSO-11.

Transalkylation of toluene with diisopropylbenzene over rey zeolite

Production of cymenes and cumene through transalkylation of toluene with diisopropylbenzene has been studied over REY zeolite. Variation of different reaction parameters and their effects on the conversion of DIPB and selectivity to cymenes and cumene are described. Concentration of cymenes are more than cumene due to successive and simultaneous reactions.

Formation ofN-methylaniline by transalkylation of aniline withN,N-dimethylaniline over zeolite Beta

Abstract The transalkylation of aniline (A) with N,N -dimethylaniline (NNDMA) over zeolite H-Beta is described. The reaction yields N -methylaniline (NMA) as the major product with other products such as toluidine (T), N -methyltoluidine (NMT) and N,N -dimethyltoluidine (NNDMT). Conversion of NNDMA and selectivity of different products depend on reaction parameters like temperature, feed ratio, space velocity, etc. The catalytic activity of H-Beta is compared with Cs and K exchanged Beta and other two large pore zeolites H-ZSM-12 and H-Y. H-Beta shows better performance compared to the other zeolites in terms of activity, stability and selectivity. Alkali cation exchange in H-Beta results in better selectivity towards NMA with less conversion and faster deactivation.

Aniline methylation over molecular sieves

Abstract Methylation of aniline forms a range of products varying from N-alkylated to C- alkylated compounds. ALPOs and substituted ALPOs facilitate N-alkylation whereas ZSM-5 catalyse both C- and N-alkylations. ZSM-5 catalyst forms only mono methylated products. Both mono and di methylated products are formed with SAPOs and ALPOs. KY and CsY catalyse only mono methyl aniline formation. Conversions are high with ZSM-5, KY and CsY. Mechanism of reaction is proposed.

Synthesis of CoVPI-5 with bifunctional catalytic activity

A novel cobalt-substituted aluminophosphate VPI-5 with bifunctional catalytic centres is synthesized; the stability, adsorptive and catalytic properties are examined.