Zeolites H-form

C. Moreau, R. Durand, J. Duhamet, and P. Rivalier, Hydrolysis of fructose and glucose precursors in the presence of H-form zeolites, J. Carbohydr. Chem., 16 (1997) 709-714. 

C. Moreau, R. Durand, C. Pourcheron, and S. Razigade, Preparation of 5-hydro-xymethylfurfural from fructose and precursors over H-form zeolites, Ind. Crops Prod., 3 (1994) 85-90. 

Kubica et al45 also investigated the effect of platinum-modified zeolites on the decalin reaction. They found that the addition of Pt enhances the catalyst activity. The initial isomerization was increased 3 times, which can be interpreted in terms of a change in the reaction initiation. In addition to initiation by a PC step over Bronsted acid sites, as proposed for H-form zeolites, a bifunctional initiation path... 

Figure 4.23 IR spectra showing hydroxyl region ofvarious H-form zeolites. Samples...

In early 1980s, Vansant proposed the silylation method to modify zeolite channels.[46 52] The principle is to use silicanes to react with the surface hydroxygroups in H-form zeolites, and after hydrolysis the formed oxides narrow the channels so as to achieve the goal of pore-size adjustment. Figure 6.18 shows the Xe-adsorption-dynamic curves for the H-form mordenite samples silylated to various degrees. From the Figure... 

One key compound, 5-hydroxymethylfurfural, readily available with a high selectivity through dehydration of fructose and fructose precursors in the presence of H-form zeolites [2-4], is a suitable starting material for the preparation of further monomer units required for polymer applications, since containing two different functional groups at the positions 2 and 5. 

The hetero Diels-Alder reaction of dihydropyran with acrolein (Scheme 2) was performed at 0 °C without solvent in the presence of H-form zeolites [11]. The best catalysts were dealuminated HY (Si/Al = 15 62% yield of the desired adduct) and H-beta (Si/Al = 25 65 % yield). The thermal reaction at 150 °C gave the adduct in 5 % yield only. 

Scheme 2. The Diels-Alder reaction of dihydropyran with acrolein catalyzed by H-form zeolites.

An yttrium-based strong Lewis acid, prepared by treatment of aqueous solutions of yttrium nitrate and zirconyl nitrate (molar ratio 16 84) with aqueous ammonia (28%), was an active catalyst of a wide range of Diels-Alder reactions [51], Among the reactions investigated was that of acrolein with dihydropyran (Scheme 2). In contrast with reactions with H-form zeolites [11] no regio- and stereoisomers were formed. 

Diels-Alder cycloaddition reaction between dihydropyran and acrolein over various H-form zeolites. 

The Diels-Alder cycloaddition reaction of dihydropyran with acrolein was performed in the presence of various H-form zeolites such as H-Faujasites, H-p, H-Mordenites which differ both in their shape selective as well as their acidic properties. The activity of the different catalysts was determined and the reaction products were identified. High 3delds in cycloadduct were obtained over dealuminated HY (Si/Al=15) and Hp (Si/Al=25) compared to HM (Si/Al=10). These results were accounted for in terms of acidity, shape selectivity and microporosity vs mesoporosity properties. The activity and the regioselectivity were then discussed in terms of frontier orbital interactions on the basis of MNDO calculations for thermal and catalyzed reactions by complexing the diene and the dienophile with Bronsted and Lewis acidic sites. From these calculations, Bronsted acidic sites appeared to be more efficient than Lewis acidic sites to achieve Diels-Alder reactions. 

In order to get more information on these two effects we have performed the Diels-Alder reaction between dihych opyi an and acrolein in the presence of various H-form zeolites such as H-faujasites, H-(t and H-mordenites. This reaction was reported to proceed with difficulty under thermal conditions in the absence of catalyst (11). The catalysts tested in this work differ both in their shape selective as well as their acidic properties. On the other hand, molecular orbital calculations (MNDO) have been performed to account for the experimental results on the uncatalyzed and catalyzed reactions. 

There has been some work on compressing the above process to one step using a solid base whose dehydration capability may be due to Lewis acid sites, e.g., alkali-exchanged zeolites. These attempts do not appear to have resulted in reasonable selectivities, because further dehydration and condensation reactions occur. An exception is the synthesis of methyl or phenyl vinylketones by condensation of a precursor methylketone with methanol/02 or formaldehyde. This process can take place with >95% selectivity at <20% conversion on Fe/Ag/AhOs at 600-650 K, or at >70% conversion with a secondary amine hydrochloride ( 40/1 aldehyde/amine)/Nb205 catalyst mixture at 390-420 K, or at lower selectivity ( 40-50%) but almost complete conversion using typical H-form zeolites at 670-730 K. ... 

P-06 - Selective hydroxy ethylation of furfuryl alcohol with aqueous acetaldehyde in the presence of H-form zeolites... 

As a further example, a,j8-unsaturated carbonyl compounds possess two sites which can undergo reduction the carbonyl group and the adjacent C—C-double bond. While an abundant hterature is available on the selective reduction of the carbonyl group, often achieved with relative ease, the selective hydrogenation of the double bond suffers from the lack of simple methods using practical chemicals. Selective ionic hydrogenation of ,j8-unsaturated carbonyl compounds with cyclohexane was previously known to proceed only in superacidic conditions due to the necessity of dicationic, superelec-trophilic activation of the enones. H-form zeolites with acidity well below superacidity are however also able to induce the reduction of o j8-unsaturated carbonyl compounds with cyclohexane, in analogy, or sometimes even better than the parent , superacid mediated reactions. ... 

Briiggemann TC, Przybylski M-D, Balaji SP, Kell FJ (2010) Theoretical investigation of the mechanism of the selective catalytic reduction of nitrogen dioxide with ammonia on H-form zeolites and the role of nitric and nitrous acids as intermediates. J Phys Chem C 114 6567-6587... 

The H-form and Pd-containing mordenites were studied by FTIR [06KI], The same typical bands in natural and H-form zeolites were fonnd. 

Eng J, Bartholomew C H (1997) Kinetic and mechanistic study of NO reduction by NH3 over H-form zeolites. 1. Kinetic and mechanistic insights into NO reduction over H-ZSM-5. J. Catal. 171 (1) 14-26. 

Hamada H, Kintaichi Y, Sasaki M, Ito T, Tabata M (1990) Highly selective reduction of nitrogen oxides with hydrocarbons over H-form zeolite catalysts in oxygen-rich atmosphere. 

Eng J, Bartholomew CH (1997) Kinetic and Mechanistic Study of NOx Reduction by NH3 over H-Form Zeolites. II. Semi-Steady-State and In Situ FTIR Studies. J. Catal. 171 27-44... 

Among a series of typical solid acid catalysts such as H-form zeolite, sulfated zirconia, sulfo-nated activated carbon, and Amberlyst polymer-based materials, sulfonated activated carbon showed a remarkably high yield of 40.5% of glucose [153]. 

Moreau C, Durand R, Pourcheron C, Razigade S. Preparation of 5-hydroxymethylfurfural from finetose and precursors over H-form zeolites. Ind Crops Prod 1994 3 85-90. 

Moreau C, Durand R, Duhamet J, Rivaher P. Hydrolysis of finetose and glueose precursors in the presence of H-form zeolites 1. J Carbohydr Chem 1997 16 709-14. 

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