Polymer heterogeneous catalysts

Liu, F., Wang, L. Sun, Q., Zhu, L., Meng, X., Xiao, F.S. 2012. Transesterification catalysed by ionic liquids on superhydrophobic mesoporous polymers Heterogeneous catalysts that are faster than homogeneous catalysts, y. Am. Chem. Soc. 134 16948-16950. 

In the Institut Fransais du Petrc le process (62), ethylene is dimerized into polymer-grade 1-butene (99.5% purity) suitable for the manufacture of linear low density polyethylene. It uses a homogeneous catalyst system that eliminates some of the drawbacks of heterogeneous catalysts. It also inhibits the isomerization of 1-butene to 2-butene, thus eliminating the need for superfractionation of the product (63,64). The process also uses low operating temperatures, 50—60°C, and pressures (65). 

As with organic solvents, proteins are not soluble in most of the ionic liquids when they are used as pure solvent. As a result, the enzyme is either applied in immobilized form, coupled to a support, or as a suspension in its native form. For production processes, the majority of enzymes are used as immobilized catalysts in order to facilitate handling and to improve their operational stability [24—26]. As support, either inorganic materials such as porous glass or different organic polymers are used [27]. These heterogeneous catalyst particles are subject to internal and external... 

In several papers (51, 84, 96, 104) the decrease of the polymerization rate with time was assumed to be caused by the decrease of C as a result of diffusional restrictions due to the formation of a polymer film on the catalyst surface. However, as a matter of experience in work with heterogeneous catalysts for ethylene polymerization, it is known that even for polymerization with no solvent, the formation of a solid polymer is possible at high rates (thousands of grams of polymer per gram of catalyst per hour) that are constant until large yields are reached (tens of kilograms of polymer per gram of catalyst). 

Pioneering works in this area started in the 1960s by polymer scientists like D. Ballard at ICI and Y. Yermakov at the Novosibirsk Institute of Catalysis [54,55]. The need for polymers with better properties and for better technologies (gas phase processes) has led to the development of various strategies to obtain supported catalytic systems [56-58]. Here, we will concentrate on reactions leading to basic chemicals, and a comparison between homogeneous and heterogeneous catalysts will be performed when possible. 

To assess the utility of this resin, we chose to employ it in the evaluation of the heterogeneity of a commercial polymer-entrapped Pd(OAc)2 precatalyst, Pd-EnCat, also sold by Reaxa. This precatalyst was designed with the goal of providing a heterogeneous catalyst that would allow simple removal of palladium from reactions (24-26). PVPy and QTU were first used as poisons in the Heck reaction of iodobenzene and n-butyl acrylate in DMF using PdfC as the palladium... 

Most of the supports so far studied are conventional in the field of catalysis. Some new kinds of support have emerged including mesostructured materials,193 dendrimers, organic-inorganic hybrids, and natural polymers such as polysaccharides or polyaminoacids. Nevertheless, at the moment, supported catalysts still suffer from relatively poor stability when compared to classical heterogeneous catalysts, and from limited activity when compared to homogeneous catalysts. The driving force for this research is thus to make up some of these deficits. 

---