Macroporous catalytic application

Scheme 10.4 Catalytic application of the commercially available macroporous Amberlyst-15.

Recent examples, for instance, of the catalytic application of the commercially available macroporous Amberlyst-15 include the Michael addition of pyrroles to a,P-unsaturated ketones (Scheme 10.4) [48]. In this process, the acid ion exchange resin (dry, 10% w/w) allows on to obtain mono and dialkylated pyrroles 5 and 6 in reasonable yields. Similarly, this catalyst (dry, 30% w/w) can catalyze the aza-Michael reaction of amines with a,P-unsaturated ketones, esters and nitriles to afford 7 in 75-95% yields under solvent-free conditions. Interestingly, yields were significantly lower using typical solvents such as DCM (dichloromethane), CH3CN, THF, DMF or EtOH [49], Recycling the catalyst is possible in both cases, but a smooth decrease in the yield is observed for each new run. 

For many catalytic applications, it may be desirable to furnish catalysts or carriers with a high portion of macropores to enhance diffusional transport of reactants. Unfortunately, the mechanical strength of the bodies decreases with increasing porosity and with increasing size of the powder particles employed [5, 7]. For an agglomerated body composed... 

New applications of zeolite adsorption developed recently for separation and purification processes are reviewed. Major commercial processes are discussed in areas of hydrocarbon separation, drying gases and liquids, separation and purification of industrial streams, pollution control, and nonregenerative applications. Special emphasis is placed on important commercial processes and potentially important applications. Important properties of zeolite adsorbents for these applications are adsorption capacity and selectivity, adsorption and desorption rate, physical strength and attrition resistance, low catalytic activity, thermal-hydrothermal and chemical stabilityy and particle size and shape. Apparent bulk density is important because it is related to adsorptive capacity per unit volume and to the rate of adsorption-desorption. However, more important factors controlling the raJtes are crystal size and macropore size distribution. 

The diameter or the radius of the pores is one of the most important geometric characteristic of porous solids. In terms of lUPAC nomenclature, we can have macropores (mean pore size greater than 5 x 10 m), mesopores (between 5 x 10 and 2 x 10 m) and micropores (less than 2 x 10 m). The analysis of species transport inside the porous structure is very important for the detailed description of many unit operations or applications among them we can mention suspension filtration, solid drying and humidification, membrane processes (dialysis, osmosis, gaseous permeation. ), flow in catalytic beds, ion exchange, adsorp-... 

The synthesis of ordered macroporous crystalline materials has been attracting much attention. Walls of macroporous materials are larger than those of mesoporous materials, and this macroporosity can be introduced into a wide variety of transition metal oxides. Potential applications of these materials include photonic materials, catalysts and electrode materials. The ordering scale is close to the wavelength of light, and interest has therefore been shown in photonic materials. In some cases, introduction of macroporosity increases the surface area, and these materials show better catalytic performance than that of nonporous materials. Similar to mesoporous materials, macropores are favoured for diffusion of reactants compared with nonporous materials and many applications, such as in a Li battery electrode, have been reported. 

Inorganic porous materials have been quickly developed during the past half century, and have found wide applications in fields such as catalytic, adsorbent, electronic, and environmental technologies. Porous materials are classified into microporous, mesoporous, and macroporous materials according to their pore size. Microporous materials have pore diameters below 2nm, and macroporous materials have pore diameter greater than 50 nm, with mesoporous materials lying in between [1] (Figure 8.1). 

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