Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Abstract

Microporous crystals of zeolites such as Y, Beta, and ZSM-5 are widely used commercial catalysts, but their applications are strongly limited by their small pore sizes. Recent progress in solving this is used to ordered mesoporous materials such as MCM-41, HMS, and SBA-15. These mesoporous materials have pore diameters of 2.0-30 nm and exhibit good catalytic properties for the catalytic conversion of bulky reactants. However, when compared with microporous crystals of zeolites, the catalytic activity and hydrothermal stability are relatively low, which severely hinders their practical applications in industrial catalytic reactions such as petroleum cracking. The relatively low catalytic activity and hydrothermal stability can be attributed to the amorphous nature of the mesoporous walls. In this account, we systemically review the routes for improving catalytic activity and hydrothermal stability of mesoporous materials, which include (1) acidic sulfated zirconia supported in mesoporous materials; (2) strongly acidic and thermally stable mesostructured sulfated zirconia with tetragonal crystalline phase; (3) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in alkaline media; (4) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in strongly acidic media; (5) hydrothermally stable mesoporous titanosilicates with catalytically active titanium species in oxidations; (6) high-temperature generalized synthesis of ultrastable ordered mesoporous silica-based materials by using fluorocarbonhydrocarbon surfactant mixtures.

Removal of DDT from aqueous solutions using mesoporous silica materials

“…With MCM-41, more than half of its surface area and pore volume is lost due to its low hydrothermal stability. 32,33 …”

Materiais híbridos à base de sílica obtidos pelo método sol-gel

“…[102][103][104] Por outro lado, sílicas puras contendo estruturas de poros altamente ordenadas já são bastante conhecidas e aplicadas. Esses materiais são conhecidos por MCMs (Mesoporous Crystalline Materials) [105][106][107][108][109] e são obtidos em sistemas híbridos, usando-se agentes direcionadores de estrutura, como agentes tensoativos, que são posteriormente extraídos.…”

Rational design of single-site heterogeneous catalysts: towards high chemo-, regio- and stereoselectivity

“…For these purposes, mesoporous molecular sieves (porous materials whose pore diameters fall in the range 2-50 nm) could represent an ideal compromise to retain the advantages of a by in situ characterization methods for solid catalysts (Thomas 1997). Then, starting from the 1990s, owing to the development of silica-based mesoporous molecular sieves, larger reactant molecules, which can enter the pore network, react there and leave it, can be transformed within the inner space of porous solids (Xiao 2005;Yang et al 2009). Mesoporous silica materials, such as MCM-41, MCM-48, HMS, KIT-6, SBA-15 or SBA-16, are, indeed, ideal supports for SSHCs, since they exhibit high surface area (600-1300 m 2 g −1 ) and their inner and outer surfaces have a profusion of pendant silanol groups (generally from 1 to 3 OH groups per square nanometre) that are optimal loci for immobilizing transition metal catalytic centres (Rigutto et al 2007).…”