Process for making crystalline metallosilicates

Abstract

The present invention relates to a process for making a crystalline metallosilicate composition and comprising crystallites having an inner part (the core) and an outer part (the outer layer or shell) such that : the ratio Si / Metal is higher in the outer part than in the inner part, the crystallites have a continuous distribution of metal and silicon over the crystalline cross-section, said process comprising : a) providing an aqueous medium comprising OH- anions and a metal source, b) providing an aqueous medium comprising an inorganic source of silicon and optionally a templating agent, c) optionally providing a non aqueous liquid medium comprising optionally an organic source of silica, d) mixing the medium a), b) and the optional c) at conditions effective to partly crystallize the desired metallosilicate, e) cooling down the reaction mixture a)+b)+c) to about room temperature, f) decreasing the pH of the reaction mixture by at least 0.1 preferably by 0.3 to 4, more preferably by 0.5 to 3, g) subjecting the resulting mixture of step f) at conditions effective to continue the crystallization of the desired metallosilicate, h) recovering the desired metallosilicate, wherein at step d) in the mixture a)+b)+c), before crystallization, the ratio Si org / Si inorganic is - / SiO2 is at least 0.3, advantageously from 0.3 to 0.62, preferably from 0.31 to 0.61, more preferably from 0.32 to 0.61, very preferably from 0.33 to 0.6.

Description

technical field [0001] The present invention relates to methods of making crystalline metallosilicates (or zeolites). Zeolites have demonstrated catalytic properties for many types of hydrocarbon conversions. In addition, zeolites have been used as catalyst supports and adsorbents for various types of hydrocarbon conversion processes, as well as other applications. More precisely, the crystalline metallosilicates produced by the method of the invention comprise crystallites having a higher silicon / metal ratio on and near the outer surface than in the interior of the crystallites The silicon / metal ratio in the part. In the following description, the outer surface and a portion close to the outer surface may be referred to as an outer layer or shell, and the inner portion may be referred to as a core. Background technique [0002] Crystalline metallosilicates are ordered porous crystalline materials having a defined crystal structure as determined by x-ray diffraction, poss...

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Problems solved by technology

External surface acidity can catalyze undesired reactions that reduce product selectivity

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