Spectroscopy of the Formation of Microporous Transition Metal Ion Containing Aluminophosphates under Hydrothermal Conditions

Abstract

One of the greatest challenges of experimentalists working in the field of molecular sieve science is the understanding of the principles that determine how porous crystalline materials are formed starting from a precursor gel under hydrothermal conditions. [1] This is far from easy because hydrothermal crystallizations take place in a closed vessel, where many interactions, equilibria, and chemical processes continuously change with crystallization time. [2] The lack of knowledge about these phenomena means that a rational a priori design of novel molecular sieves is still impossible and, consequently to date, the synthesis of such materials requires a systematic and intelligent screening of the n-dimensional reaction. Recently, the concepts of combinatorial chemistry [3] and experimental design [4] have been successfully explored in order to speed up this screening process. Clearly, a more detailed understanding of the processess occurring during the synthesis of these materials is required, which can lead to a more rational approach towards zeolite syntheses. Experimental SectionReaction of N-methyldihydropyridine with carbene complexes (general procedure): A solution of N-methyldihydropyridine (3 equiv) in CH 2 Cl 2 (0.5 mL per mmol of amine) was added dropwise to a solution of carbene complex (1 equiv) in CH 2 Cl 2 (25 mL per mmol of carbene) at À 10 8C under argon . After 15 min, the ice bath was removed and the mixture was stirred at room temperature for 24 h. The solution slowly turned dark red. The solvent was evaporated under vacuum, and the residue purified by chromatography on silica gel with petroleum ether (PE)/Et 2 O as eluent.

Implementation of a combined SAXS/WAXS/QEXAFS set-up for time-resolvedin situexperiments

“…As an example of the usefulness of the applied method we show data on the crystallization of CoAPO. This system was studied previously by in situ diffuse reflectance spectroscopy and electron spin resonance (Weckhuysen et al, 2000), and more recently by independent in situ XAFS and SAXS/WAXS techniques (Grandjean et al, 2005), but since these results were not obtained during one combined measurement it was difficult to understand exactly how changes in each technique corresponded to each other, so the finer details of the crystallization process could not be understood.…”

In Situ UV Raman Spectroscopic Study on the Synthesis Mechanism of AlPO‐5

“…[13] Relatively few in situ studies have been reported in which attempts were made to follow the crystallization of practically used aluminophosphate molecular sieves. [4,6,10,11,14,15] Raman spectroscopy is a suitable technique to investigate aqueous solutions as well as solid phases of zeolite synthesis mixtures because of the low Raman scattering cross section of water. We have recently developed an apparatus capable of studying hydrothermal reactions in situ using UV Raman spectroscopy.…”

27Al and 31P NMR Investigations of Soluble Aluminophosphate Species in Alcohol–Water Mixtures

“…Aluminophosphates (AlPOs) are widely used as catalysts and molecular sieves in industrial processes [1]. Soluble aluminophosphate species, such as [Al(H 2 O) 4 (OH)(H 2 PO 4 )] + , have been suggested as nutrients for the growth of aluminophosphate molecular sieves [2].…”