R. Prins

Vapour-phase nitration of benzene over modified mordenite catalysts

Abstract Active and stable mordenite catalysts have been developed for the selective nitrobenzene production by vapour-phase nitration of benzene with 65 wt.-% HNO 3 at normal pressure and 443 K. The acidic and textural properties of commercial synthetic mordenite have been modified by different combinations of thermal and acid treatments. The physico-chemical properties of the catalysts were investigated by 27 Al and 29 Si MAS-NMR, AAS, XRD, N 2 and low pressure Ar adsorption. The catalytic activity and stability of the modified mordenite catalysts were strongly influenced by the amount and state of aluminium in the zeolite. Extra-framework aluminium species generated by thermal treatment at higher temperatures (≥973 K) induced a severe catalyst deactivation. The deactivation could almost be eliminated by subsequent acid leaching with 6 N HCl, which removed the extra-framework aluminium to a large extent, thus unblocking the pores and/or pore mouths. An optimum mordenite modification procedure was developed, resulting in highly active and selective catalysts, which retained their initial activity for at least 120 h on stream.

Isopropylation of biphenyl over dealuminated mordenite

Abstract Alkylation of biphenyl with propene in mesitylene as a solvent over a series of modified mordenite catalysts was studied in a continuous microflow reactor. Na-mordenite was modified by subjecting it to combinations of acid extraction and calcinations. Performance and selectivity for 4,4′-diisopropyl biphenyl formation of the mordenite catalysts depended on their Na content, Si/Al ratio and porous texture. Best results were obtained using a highly crystalline modified mordenite having a low sodium content, a Si/Al ratio of about 70, a secondary pore volume in mesopores of about 0.15 ml/g and a surface area in mesopores of about 30 m 2 /g. Thermal analysis showed that coke on deactivated catalysts consisted mainly of propene oligomers.

Effects of non-framework alumina in the acylation of xylene over USY

USY zeolites are active catalysts for the benzoylation of m-xylene. The activity depends on the stabilization procedure, the reaction conditions and, in particular, on the solvent and the acylating agent used. Investigation of the catalysts and the reaction mixture by elemental analysis and NMR shows that non-framework alumina species in stabilized Y catalysts interact with chloride acylating agents and become catalytically active. The active material thus formed is soluble in sulfolane and the dissolved species are active homogeneous acylation catalysts.

Vapour-Phase Nitration of Benzene over Zeolitic Catalysts

Summary Catalysts based on zeolite Y, mordenite, ZSM-5 and clinoptilolite were applied in the gas phase nitration of benzene with nitric acid. Catalyst performance depended on crystal structure, crystallinity, lattice composition, external surface area and mesoporosity. Non framework aluminium acted as a catalyst poison. Best results were obtained with a clinoptilolite based catalyst.

Benzoylation of xylenes using zeolitic catalysts

The effect of post-synthesis treatments of zeolite Y on the acylation of xylenes by benzoyl chloride has been investigated. The most active catalyst is highly crystalline material having a meso-pore structure and containing non-framework aluminium species, which shows an even higher initial activity than proton superacids. m -Xylene is the most active substrate among the three xylene isomers. Polar solvents such as sulfolane and nitrobenzene increase the reaction rate by several times, and non-polar solvents slow down the reaction.

Zeolite Catalysed Rearrangement of Aromatic Amines

Abstract The influence of reaction conditions, catalyst parameters and reactants on the rearrangement of aromatic amines to substituted methylpyridines catalysed by zeolites has been examinated. Passivation of the outer surface has been used to increase the selectivity. Experiments have been carried out with different zeolite types, with substituted anilines and with naphthylamines in order to prove a new model for the mechanism of the reaction.

Metal support Interaction

A Rh K EXAFS study showed that the rhodium particles in a Rh/Ta 2 O 5 catalyst were fully reduced and in the ‘normal’ state after reduction in H 2 at 523 K. The metal particles contained about 73 rhodium metal atoms and had a diameter of 17 A. After reduction at 858 K the catalyst was in the SMSI state. In addition to a contribution from rhodium nearest neighbours, two contributions from neighbouring tantalum ions could be detected. The tantalum ions were located in the reduced supporting oxide directly underneath the rhodium metal particles and in tantalum oxide covering the rhodium metal particles. Neither alloy formation, nor the formation of pillboxes or raftlike structures was observed.

EXAFS evidence for direct Rh-Tan+ bonding and coverage of the metal particles in a Rh/Ta2O5 SMSI catalyst

An EXAFS investigation showed that the rhodium particles in a Rh/Ta2O5 catalyst were fully reduced and in the ‘normal’ state after reduction in H2 at 523 K. After reduction at 858 K, in the SMSI state, tantalum ions could be detected in the reduced supporting oxide directly underneath the rhodium metal particles and in tantalum oxide covering the rhodium metal particles. Neither alloy formation, nor the formation of raftlike structures was observed.