Coupling agents Surface-active

Silica is unique among nonblack fillers. Its reinforcing ability is comparable to that of carbon black, especially when mixed with a suitable coupling agent, and its transparency affords many products. Additionally, it is chemically synthesized, which means that a wide range of silica (in terms of diameter, surface area, or surface activity) may be produced depending on the reaction routes and reaction conditions. 

The use of glutaric dialdehyde as a coupling agent bound the enzymes trypsin or glucose-6-phosphate dehydrogenase to the surface. A large part of the enzymic activity was retained (Fig. 4), and the activity was such that the particle-enzyme conjugate could be used in laboratory scale continuous-flow reactors. 

The immobilization process, however, can be complicated. The immobilization of an enzyme on nylon serves as a point of comparison. The first step is to activate the surface of the nylon by treating it with hydrochloric acid at room temperature for 24 hours. The partially hydrolyzed nylon is then dried in ether and stored in a desiccator overnight. The nylon is then mixed with a coupling agent [l-ethyl-3-(3-dimethyaminopropyl)] and shaken for 1 hour. The enzyme is then added and shaken overnight at 4 C. 

The use of dimethyldichlorosilane as a coupling agent for the grafting of VOx structures on the MCM-48 surface, produces a material that is simultaneously hydrophobic (inmiscible with water) and very active (all V-centers are accessible, even for water molecules and the catalytic activity for methanol oxidation has increased). The VOx surface species are grafted by the Molecular Designed Dispersion of VO(acac)2 on the silylated surface, followed by a calcination in air at 450°C. These hydrophobic MCM-48 supported VOx catalysts are stable up to 500°C and show a dramatic reduction in the leaching of the V-centers in aqueous media. Also the structural stability has improved enormously. The crystallinity of the materials does not decrease significantly, even not when the samples are subjected to a hydrothermal treatment at 160°C and 6.1 atm. pressure. 

It can be inferred from table 1 that the activity of the catalyst with the coupling agent is the highest. The selectivity for formaldehyde has decreased however and a larger amount of demethylether is formed. This is an indication for a higher surface acidity, probably caused by the V-OH groups, surrounded by an hydrophobic environment. 

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