Silica-alumina catalyst synthesis

Double-bond isomerization was once used in the multistep synthesis of isoprene developed by Goodyear.266-268 2-Methyl-1-pentene produced by the dimerization of propylene was isomerized to 2-methyl-2-pentene over a silica-alumina catalyst at 100°C. The product was cracked to isoprene and methane. Because of the lower cost of isoprene isolated from naphtha or gas oil-cracking streams, synthetic isoprene processes presently are not practiced commercially. 

Propylene Dimer. The synthesis of isoprene from propylene (109,110) is a three-step process. The propylene is dimerized to 2-methyl-1-pentene, which is then isomerized to 2-methyl-2-pentene in the vapor phase over silica alumina catalyst. The last step is the pyrolysis of 2-methyl-2-pentene in a cracking furnace in the presence of (NH4)2S (111,112). Isoprene is recovered from the resulting mixture by conventional distillation. 

Catalysis and reaction engineering became entwined in the late 1930s with the realization that the cracking of petroleum could be achieved most effectively using silica-alumina catalysts. With time, the connection between these two areas grew stronger as more and more catalytic processes were developed for the refining of petroleum, the production of petrochemicals, and the synthesis of polymers. 

H. Nanbu, Y. Ishihara, H. Homna, T. Takesue, and T. Ikemura, Synthesis of Branched Polyethylene by Catalytic Degradation-Isomerization of High Density Polyethylene in the Presence of Silica-Alumina Catalyst, Chem. Soc. Jpn., 765-770 (1987). 

Alkenes are not present to a significant extent in crude petroleum. They are essential starting compounds for the synthesis of organic chemicals and polymers, so their production from alkanes is of great importance. One way to produce alkenes is by cracking the petroleum by heat or with catalysts. In catalytic cracking, the heavier fractions from the distillation column (compounds of Cn or higher) are passed over a silica-alumina catalyst at temperatures of 450°C to 550°C. Reactions such as... 

The conventional amorphous silica-alumina catalysts have been substituted here by zeolites, especially of the H-ZSM-5 type [49J. Higher yields and higher pyridinc/p-picoline ratios arc obtained with zeolite catalysis. The micropores will reduce the formation of higher alkylated pyridines. The zeolites can be further improved by incorporating metal oxides (e.g. Pb, Tl, Co) or noble metals or by applying both types of promoters. As an example, a Pb-MFI catalyst, operated at 450 °C in a fixed bed reactor and fed with CH2 O/CH3CHO/NH3 in a 1.0 2.0 4.0 molar ratio gave 79 % total pyridines with a pyridine/p-picoline ratio of 7.5. Also zeolites MCM-22 and Beta [50] perform well in combined pyridine/p-picoline synthesis. 

The key stage is the alkylation of cumene. From its reaction in the liquid phase at 300°C in the presence of a silica/alumina catalyst with 3 moles of propene the 1,4-isomer required for hydroquinone is separated by fractionation (ref.30) and the mixture of 1,2- and 1,3-di-isopropylbenzenes together with the tri-isopropyl isomer equilibrated with benzene at 270°C with the same catalyst to enrich the proportion of the 1,3-compound required for the synthesis of resorcinol. The sequence of steps for hydroquinone is shown. By-product 4-isopropylphenol is mostly reoxidised and recycled giving a total yield of 71% based on di-isopropylbenzene (ref.31). 

Al-Si-TUD-1 can be a stand-alone cracking catalyst, much like traditional amorphous silica-alumina catalysts, albeit with higher surface area/porosity. Since molecular intimacy is required for the silica and alumina to be effective, the most successful synthesis approach here used TEOS and AIP - critical in forming monomeric species. A simple indicator for nonuniformity is a bimodal pore size distribution, indicative of two separate phases. 

Cammidge, A.N. Baines, N.J. Bellingham, R.K. Synthesis of heterogeneous palladium catalyst assemblies by molecular imprinting. Chem. Commun. 2001, 2588-2589. Morihara, K. Kurihara, S. Suzuki, J. Footprint catalysis. I. A new method for designing tailor-made catalysts with substrate specificity silica (alumina) catalysts for butanolysis of benzoic anhydride. Bull. Chem. Soc. Jpn. 1988, 61, 3991-3998. Morihara, K. Nishihata, E. Kojima, M. Miyake, S. Footprint catalysis. II. molecular recognition of footprint catalytic sites. Bull. Chem. Soc. Jpn. 1988, 61, 3999-4003. Shimada, T. Makanishi, K. Morihara, K. Footprint catalysis. IV. structural effects of templates on catalytic behavior of imprinted footprint cavities. Bull. Chem. Soc. Jpn. 1992, 65, 954-958. 

As already mentioned, the acidity of the HY zeolite precludes its use as a support for Fe3(C0)- 29 then iron particles. The same behaviour is observed for Fe3(C0) 2 silica alumina system. This material, when decomposed at 200°C is not an efficient catalyst for F-T synthesis and only C-j-C products are... 

After the catalytic runs no modification of mean particle size is observed for this last system. Conversly, Ru CO) deposited on silica-alumina is readily decomposed at 200°C to metallic particles of 1 nm mean size which are also catalysts for the F-T synthesis. The catalytic activity at 200°C is C i one tenth of the Y zeolite supported ones and methane is practically the only hydrocarbon formed. Electron microscopy examination of the catalyst after reaction reveals a drastic sintering of the... 

As catalysis proceeds at the surface, a catalyst should preferably consist of small particles with a high fraction of surface atoms. This is often achieved by dispersing particles on porous supports such as silica, alumina, titania or carbon (see Fig. 1.2). Unsupported catalysts are also in use. The iron catalysts for ammonia synthesis and CO hydrogenation (the Fischer-Tropsch synthesis) or the mixed metal oxide catalysts for production of acrylonitrile from propylene and ammonia form examples. 

Although beyond the scope of this book, a vast amount of work has been directed to supporting homogeneous catalysts on solid supports including silica, alumina and zeolites, and functionalized dendrimers and polymers [19]. These give rise to so-called solid-liquid biphasic catalysis and in cases where the substrate and product are both liquids or gases then co-solvents are not always required. In many ways solvent-free synthesis represents the ideal method but currently solvent-free methods can only be applied to a limited number of reactions [20],... 

Catalysts employed in this study are zirconium(lV)-hydrides on oxide support (silica, silica-alumina and alumina). Their synthesis is described above. We present here some transformations or modifications of polystyrene, linear alkanes and polyethylene with Zr-H catalyst... 

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