Analogues of zeolite molecular sieves

Analogues of zeolite molecular sieves

373 (i) Catalytic transformations of hydrocarbons and oxygenated comDounds; papers ranging from-isobuteneproduction (see followinq item) to toluene st...

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373 (i) Catalytic transformations of hydrocarbons and oxygenated comDounds; papers ranging from-isobuteneproduction (see followinq item) to toluene steam dealkylation.’ (ii) Oxidation reactions and related catalysts; papers including selective oxidation of propylene and the production of pyridines from propylene by ammoxidation. (iii) Hydrogenation reactions and related catalysts; two papers on rhodium catalysts and one on selective hydrogenation of vegetable oils. (iv) Structures of catalytically active solids; mostly papers on mixed oxide catalysts but also on supported Pt and electrocatalysis. (v) Surfaces of catalytically active solids; papers describinq the use of techniques such as IR, Xi% and calorimetry to characterise the surfaces of solids. Although the conference language was Italian, a set of extended abstracts in English was available. The group hopes that it will soon be in a position to run an international conference in Italy. Production

of Pure Isobutene

Workers from Assoreni have described (G. Manara, V. Fattore, M. Taramasso and B. Notari, US patent 4,254,296 and Fifth International Conference on Zeolites, Naples, 1980, p.40) a new molecular sieve borosilicate having zeolitic crystalline structure. The use of this catalyst in a new route for the separation of pure isobutene was recentlydescribed in a paper by B. Notari, V. Fattore and M. Massi Mauri given at the 3rd Italian Conference on Catalysis (Rimini, September 1982). The reaction used is the decomposition of methyl tertiary butyl ether (MTBE), one previously carried out over a surface-modified y-Al203 catalyst (see Hydrocarbon Processing, (1981), 101). The advantage of the borosilicate is that it is non-acidic in character and that it therefore does not catalyse undesirable side-reactions such as the dehydration of methanol to dimethylether or the selfalkylation of isobutene to Droduce oligomers,as found with the'modified alumina. The MTBE is Droduced bv reaction of methanol with C4 miitures. Previous methods of producing pure isobutene included its extraction

oy(ll#lm-

Volume 5 No. 3 - March 1993

from C4 cuts using sulphuric acid or molecular sieves or the dehydration of tertiary butyl alcohol. Is is used in auantities of about 1 million tons per'year in the production of polyiso-butene, methacrylates and fine chemicals. Analogues

of Zeolite Molecular

Sieves

Union Carbide workers have recently reported (J.Amer.Chem.Soc., 104 (19821 11461 that a series of scne twenty aluminophosphate compounds, most of which are microporous, may be prepared by hydrothermal synthesis at 100°-250°C in the presence of an organic amine or a quaternary ammonium salt which is trapped within the cavities of the solids and which determines, to some extent, the pore sizes (see also Catalytica Highlights, 8 (1982) No.2). Most of the three dimensional microporous compounds formed have high thermal stabilities and remain crystalline at the temperatures at which the organic templates are removed. The new aluminophosphates are neutral and carry no associatedcations; they exhibit hydrophilic behaviours between those of ionic zeolites and siliceous zeolites such as silicalite and ZSM-5. Loewenstein's

Rule Rules

Earlv results on zeolite-A maaicangle 29s; NMR led to reports con- cludina that Al-O-Al bridaes exist in certain zeolites, in violation of Loewenstein's rule. Careful examination of these data and a study of the 29Si magic-angle NMR spectra of other zeolites have shown that this interpretation was erroneous. The Si/Al ratios measured by NMR techniques for a wide range of faujasites are in agreement with ratios measured independently by X-ray emission techniques and with an empirical equation valid only in the absence of Al-O-Al bonds. The A-type'zeolites also obey this equation. The 29Si chemical shift previously attributed to the presence of Al-O-Al bonds is now thought to be due to nearly linear Si-O-Al bonds [see Nature, 298 (1982) 455 and J.Chem.Soc., Faraday Trans. II, 78 (1982) 10251. These recent developments and other advances in zeolite science are analyzed in a multi-client study published by Catalytica Associates, Inc., 3255 Scott