Clays clay-based catalysts

Previous studies carried out with clay based catalysts pillared by Fe hydroxo complexes [13] or mixed (Al-Cu or Al-Fe) complexes, have shown that the mixed PILCs lead to the most promising results for organic compounds total oxidation in water, by using hydrogen peroxide as oxidant [14-16],... 

Houdry The first catalytic petroleum cracking process, based on an invention by E. J. Houdiy in 1927, which was developed and commercialized by the Houdry Process Corporation. The process was piloted by the Vacuum Oil Company, Paulsboro, NJ, in the early 1930s. The catalyst was contained in a fixed bed. The first successful catalyst was an aluminosilicate mineral. Subsequently, other related catalysts were developed by Houdry in the United States, by I. G. Farbenindustrie in Germany, and by Imperial Chemical Industries in England. After World War II, the clay-based catalysts were replaced by a variety of synthetic catalysts, many based on alumino-silicates. Later, these too were replaced by zeolites. U.S. Patents 1,837,963 1,957,648 1,957,649. 

Mordenite etc. Dodecatungstophosphoric acid (DTPA) and the ion exchange resin catalysts showed maximum activities. Clay based catalysts and sulphated zirconia showed a moderate activity. Zeolites did not demonstrate any activity to the reaction due to pore size restriction. A 100% selectivity towards the ortho product (l-acetyl-2-methoxy naphthalene) was observed for almost all the reactions for all the catalysts. The para product (2-methoxy-6-acetyl naphthalene) was formed when the aluminium chloride was used as a homogeneous catalyst with nitrobenzene as the solvent. The reaction product was isolated and conformed by the melting point, FT-IR, H-NMR, etc. The reaction is intraparticle diffusion limited. A different catalyst would be required to get p-product selectively. 

The high surface area of clays also makes them particularly attractive as catalyst and reagent supports. Discussion in this chapter will be largely confined to clay-based catalysts in which metal complexes or other ions are specifically incorporated in the clay matrix. Other clay-based catalytic materials will be discussed in Chapter 4. 

The manufacture of these clay-based catalysts consisted of crushing, drying and sizing the raw clay. The sized clay was then formed into slurry followed by washing. The sized clay was dewatered, dried, ground and sized as the final steps in the process (55). This clay catalyst could then be further formed into cylinders or beads depending on the final usage. 

Scheme 11.3 Schematic representation of the polymerization behavior with in-situ protocol, (upper) and tunnel protocol (bottom) clay-based catalysts.

Herney-Ramfrez, J. and Madeira, L. (2010). Use of Pillared Clay-based Catalysts for Wastewater Treatment Through Fenton-hke Processes, in A. GU, S. Korili, R. Trujillano, et al. (eds). Pillared Clays and Related Catalysts, Springer, Heidelberg, Germany, pp. 129—166. 

Preparation by acylation of resorcinol with phenylacetyl chloride in boiling ethylene dichloride (84°), using a series of clay based catalysts (KSF, KSF/0, KPIO, KIO, KO, KS) (65-81%) [5252], (60%) [5253]. 

Concerning other metals, Sonogashira coupling products have also been observed in the reaction of Ag(l)-carbenes [133] and Au(I)-supported carbenes [134] in low to moderate yields, but only under harsh conditions (more than 100°C). In this regard, NHC based catalysts for Sonogashira reactions have been supported on different materials that include clays [135], polymers [136] and peptides [137]. 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

Catalytic cracking is a process that is currently performed exclusively over fluidized catalyst beds. The fluid catalytic cracking (FCC) process was introduced in 1942 and at that time replaced the conventional moving bed processes. These early processes were based on acid-treated clays as acidic catalysts. The replacement of the amorphous aluminosilicate catalysts by Faujasite-type zeolites in the early-1960s is regarded as a major improvement in FCC performance. The new acidic catalysts had a remarkable activity and produced substantially higher yields than the old ones. 

Table III summarizes the parameters that affect Brrfnsted acid-catalyzed surface reactions. The range of reaction conditions investigated varies widely, from extreme dehydration at high temperatures in studies on the use of clay minerals as industrial catalysts, to fully saturated at ambient temperatures. Table IV lists reactions that have been shown or suggested to be promoted by Br nsted acidity of clay mineral surfaces along with representative examples. Studies have been concerned with the hydrolysis of organophosphate pesticides (70-72), triazines (73), or chemicals which specifically probe neutral, acid-, and base-catalyzed hydrolysis (74). Other reactions have been studied in the context of diagenesis or catagenesis of biological markers (22-24) or of chemical synthesis using clays as the catalysts (34, 36). Mechanistic interpretations of such reactions can be found in the comprehensive review by Solomon and Hawthorne (37).

Examples of the application of recyclable solid base catalysts are far fewer than for solid acids [103]. This is probably because acid-catalyzed reactions are much more common in the production of commodity chemicals. The various categories of solid bases that have been reported are analogous to the solid acids described in the preceding sections and include anionic clays, basic zeolites and mesoporous silicas grafted with pendant organic bases. 

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