Support monolithic

Some catalyst supports rely on a relatively low surface area stmctural member coated with a layer of a higher surface area support material. The automotive catalytic converter monolith support is an example of this technology. In this appHcation, a central core of multichanneled, low surface area, extmded ceramic about 10 cm in diameter is coated with high surface area partially hydrated alumina onto which are deposited small amounts of precious metals as the active catalytic species. 

Only by using the carrier can the catalyst be sufficiently active because the majority of appHcations require 10 to 100 m /g of surface area (20). Surface areas for a typical monolith support stmcture and a carrier are given (20). 

Fig. 11. Monolithic supports, (a) American Lava Thermaeomb. (b) Coming W-l-(c) DuPont Torvex. (d) Kalichemie.

In order to speed up the log P estimate by gradient RPLC, several solutions were investigated, i.e. fast gradient elution obtained with the help of monolithic supports or short columns and the use of mass spectrometry (MS). 

In this study, chromatographic experiments were 10 times faster with the monolithic column and results were equivalent to those obtained with the silica-based columns. This approach could be further optimized with faster gradient since flow rate should be increased by a factor 3 or 7 compared to conventional Cig supports [61, 62] and gradient time reduced by the same factor [63] to fully exploit the potential of monolithic supports. 

Table 1. Main characteristics of different monolithic supports... 

The main characteristics of ah these types of monolithic supports are summarized in the Table 1. 

In addition, it has been shown that other enzymes such as trypsin can be successfully immobilized and used for the conversion of substrates with higher molecular masses [76]. Petro et al. [94] compared the activity of trypsin immobilized on macroporous beads and on monolithic supports. They were able to show that the catalytic activity of trypsin bound to a monolith was much higher and resulted in a much higher throughput. Other enzymes such as invertase [76] and... 

In order to understand monolithic supports and the effects of polymerization parameters, a brief description of the general construction of a monolith in terms of microstructure, backbone and relevant abbreviations is given in Fig. 8.1 [63, 64]. As can be deduced therefrom, monoliths consist of interconnected microstrac-ture-forming microglobules, which are characterized by a certain diameter dp) and microporosity (gp). In addition, the monolith is characterized by an inter-microglobule void volume sfj, which is mainly responsible for the backpressure at a certain flow rate. The sum of gp and g directly translates into the total porosity gf. 

Tab. 8.5 Functional monomers used for surface-grafting of monolithic supports.

Scheme 8.8 Synthesis of a monolith-supported second generation catalyst immobilized via the NHC-ligand. R = adamantyl, mesityl.

Alternatively, monolith-supported second generation Crubbs catalysts containing unsaturated (e.g. IMes) or saturated (e.g. SIMes) NHCs [5] can be prepared by a synthetic protocol summarized in Scheme 8.9. Surface-derivatization of a monolith was carried out with 7-oxanorborn-2-enedicarboxylic anhydride followed by conversion of the grafted poly(anhydride) into the corresponding poly-silver salt. 

Poly-(N,N-dipyrid-2-yl-7-oxanorborn-2-en-5-ylcarbamido PdCl2)-grafted Monolithic Supports for Heck Reactions... 

A structured ruthenium catalyst (metal monolith supported) was investigated by Rabe et al. [70] in the ATR of methane using pure oxygen as oxidant. The catalytic activity tests were carried out at low temperature (<800 ° C) and high steam-to-carbon ratios (between 1.3 and 4). It was found that the lower operating temperature reduced the overall methane conversion and thus the reforming efficiency. However, the catalyst was stable during time on-stream tests without apparent carbon formation. 

The huge variety of different monolithic supports being introduced for HPLC applications can generally be divided into two main classes monoliths based on organic precursors and monoliths based on inorganic precursors. 

To conclude, it seems to be obvious that (meth)acrylate monolithic supports that can be prepared by polymerization of a huge variety of chemically different monomers are very versatile due to their broad diversity of surface chemistries. 

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