Solid catalysts chemical modification

Due to its large availability and low cost, native starch has been used for a long time in the preparation of different end-products. To obtain specific properties, native starch has to be chemically or enzymatically modified. Because native starch is an insoluble, partially crystallized solid polymer, chemical modifications are difficult to achieve and require the use of soluble catalysts. We have achieved two catalytic modifications of native starch (i) selective oxidation to obtain carboxyl and carbonyl functions, thus making starch more hydrophilic (8), and (ii) telomerisation of butadiene with the hydroxyl groups of the glucoside units, thus providing more hydrophobic material (8,9). 

The chemical modification of the surface of solids has led to increased possibilities in a number of fields on laboratory as well as on industrial scale. Applications of modified silicas may be classified according to the field in which they are of interest. In each field the interaction with a specific type of molecules is effectuated. In the analytical field organic compounds and metal ions are selectively adsorbed. The chemical field aims at the immobilization of metal complexes for use as catalyst... 

Easton, E.B. et al.. Chemical modification of proton exchange membrane fuel cell catalysts with a sulfonated silane, Flectrochem. Solid-State Lett., 4, A59, 2001. 

Because the catalysts widely used in petroleum and chemical industries are inorganic solids, the activation and modification of different kinds of solid catalysts by shock waves were investigated by Xu and colleagues [3,4],... 

Chemical surface modification techniques provide effective routes to mesoporous solid catalysts which are active in various liquid phase organic reactions including selective oxidations, nucleophilic substitutions, and oevenagel reactions. 

Sulfonic acid resins can be used as solid catalysts for esterifications and other acid-catalyzed reactions. Am-berlyst 15 was a more effective catalyst for the preparation of esters of phenethyl alcohol and cyclohexanol than sulfated zirconia, an acid clay, and dodecatungstophos-phoric acid.113 (Amberlyst and Amberlite are trademarks of Rohm Haas.) (See Chap. 6 for more detail on solid acids and bases.) The same catalyst gave 86-96% yields of hydroxyesters when a lactone was stored with a hy-droxyacid.114 Diols can be monoacylated in 58-92% yields by transesterification with ethyl propionate in the presence of Dowex 50W (a product of the Dow Chemical Co.).115 Modification of the sulfonic acid resin with 2-mercaptoethylamine produced a catalyst for the reaction of phenol with acetone to produce bisphenol A (5.30) in 99.5% yield.116 After 20 cycles the yield was still 98.7%. When used as catalysts, ion-exchange resins can last for 6 months to 2 years. 

Silica exists in a broad variety of forms, in spite of its simple chemical formula. This diversity is particularly true for divided silicas, each form of which is characterized by a particular structure (crystalline or amorphous) and specific physicochemical surface properties. The variety results in a broad set of applications, such as chromatography, dehydration, polymer reinforcement, gelification of liquids, thermal isolation, liquid-crystal posting, fluidification of powders, and catalysts. The properties of these materials can of course be expected to be related to their surface chemistry and hence to their surface free energy and energetic homogeneity as well. This chapter examines the evolution of these different characteristics as a function not only of the nature of the silica (i.e., amorphous or crystalline), but also as a function of its mode of synthesis their evolution upon modification of the surface chemistry of the solids by chemical or heat treatment is also followed. 

An important example, in the context of the synthesis of fine chemicals is the use of chiral modifiers to promote enantioselective catalysis, e. g. of hydrogenations as described in Section 8.11. The mechanism of enantioselection is often poorly understood. A better understanding of the underlying mechanisms of chiral modification could broaden the scope of enantioselective hydrogenation over solid catalysts, which is currently rather limited. 

Signoretto M, Oliva L, Pinna F, Strukul G (2001) Synthesis of sulfated-zirconia aerogel Effect of the chemical modification of precursor on catalyst porosity. J Non-Cryst Solids 290 145-152... 

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