Heterogeneous catalysis organic media

In recent years, the use of heterogeneous catalysis has received useful applications in various organic transformations due to several advantages over conventional homogeneous catalysis. Several solid acid catalysts [108] such as Amberlyst [109], solid-supported fluoroboric acid [110], polyaniline sulfate [111], polystyrene-supported sulfonic acids [112], sulfated zirconia [113], and silica [114] in conjunction with other greener techniques such as MW, US, environmentally benign solvents, solvent-free conditions, and so on have been screened, evaluated, and compared with respect to yields, reaction time, reaction temperature, ease of purification, reusability, toxicity, and other hazards for sustained applications. Many of these efforts have found applications in the medium ring-sized heterocycles such as oxepines, azepines, diazepines, oxazepines, thiazepines, and so on. 

This ratio is vahd when the system operates close to thermodynamic equihbrium. It is, however, typical for heterogeneous catalysis to occur far from equihbrium in an open, nonlinear, dissipative, distributed, and multiparametric medium. Thus heterogeneous catalytic reactions exhibit diverse nonlinear phenomena the multiplicity of steady states (stable and unstable) hysteresis phenomena the ignition and extinction of the process critical phenomena phase transitions a high sensitivity of the process to changes in the parameters oscillations and wave phenomena chaotic regimes the formation of dissipative structures and seh organization phenomena. 

Carbocatalysis shows differences with respect to organocatalysis, since in the last case an organic molecule, for example amines, is used as active sites. The organic molecule can be soluble in the reaction medium, but it can also be anchored onto an insoluble, large-surface area solid, converting a homogeneous catalyst into a heterogeneous catalyst. In contrast carbocatalysis is based in the use of materials and not in the use of molecules. However, it is clear that both areas of catalysis may have some similarities with respect to the nature of the active centers, the low thermal stability in... 

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