Direct Synthesis of Well-Ordered and Unusually Reactive FeSBA-15 Mesoporous Molecular Sieves

Abstract

Large-pore hexagonal SBA-15 molecular sieves partially substituted with iron(III) have been synthesized for the first time in highly acidic media. The degree of iron(III) incorporation into SBA-15 can easily be controlled by a simple adjustment of the molar ratio of water and hydrochloric acid. All the materials have been characterized by XRD, N 2 adsorption, UV-Vis DRS, ESR, and XANES spectroscopy. The characterization of the FeSBA-15 materials by UV-Vis DRS, ESR, and XANES spectroscopies suggests that the iron atoms are highly dispersed and mostly occupy isolated tetrahedral sites. XANES studies revealed that the proportion of tetrahedrally coordinated Fe atoms decreases with decreasing n Si /n Fe ratios. Benzylation of benzene (or substituted benzenes) using benzyl chloride as the alkylating agent over FeSBA-15 with different n Si /n Fe ratios was investigated as was the same reaction using AlSBA-15 as catalyst. The influence of parameters such as reaction temperature, reactant feed ratio, and the presence of electrondonating substituents on the activity and selectivity of AlSBA-15 was studied. Under optimized reaction conditions, the FeSBA-15 catalyst showed a superior catalytic performance in the benzylation of benzene and other aromatics using benzyl chloride, with a clean conversion of benzyl chloride to the monoalkylated product (100% selectivity) with a very high rate constant when compared to other mesoporous materials such as AlSBA-15 and FeHMS. Interestingly, use of FeSBA-15(21) resulted in quantitative conversion of benzyl chloride with a high rate constant of 2420.5 × 10 -4 min -1 under the optimized reaction conditions.

Controlling Reaction Pathways for Alcohol Dehydration and Dehydrogenation over FeSBA-15 Catalysts

“…Clearly, these sites are not affected by the presence of a small amount of Fe embedded in silica. Such isolated Fe 3þ species that lead to the presence of Brønsted acid reaction sites have also been reported to be active for benzylation of benzene and other aromatics using benzyl chloride [22,23] and the dehydration of propanol [24,30]. Agglomerated iron oxide clusters in the mesopores of FeSBA-15(4) increase the acetaldehyde yield from 2.7% to 8.5%.…”

“…Mesoporous materials such as those of the SBA-n or M41S families offer opportunities for well-tailored, improved access to their well-defined pores which are larger than those typically found in zeolites [19] Further functionalizaton of the silica surface can be brought about by incorporation of isolated metal ions or small metal oxide clusters [20]. For example, iron-containing mesoporous materials have been reported to show good catalytic performance in vapor-phase t-butylation of phenol, liquid-phase benzylation of benzene by benzyl chloride and decomposition of isopropanol [21][22][23][24].…”

Fabrication and textural characterization of nanoporous carbon electrodes embedded with CuO nanoparticles for supercapacitors

“…Several reports on the fabrication of transition-metal-oxide-supported nanoporous materials are available in the literature [30][31][32][33][34][35]. However, most of the methods involve the post synthetic impregnation of the metal oxide nanoparticles inside the mesochannels of the support, which has a limited efficiency.…”

Promoted and Controllable Self-Assembly of Hydrolyzed Siloxane and Triblock Copolymer under Organic Polyhydroxy Acids

“…Furthermore, strong acidities suppress the direct incorporation of heterogeneous atoms into the framework of the silica to obtain functionalized catalysts. [14][15][16] Therefore, some attempts have been made to synthesize SBA-15 under moderate conditions. [17][18][19][20][21][22] However, weak acidities seem difficult to afford quick phase separation of mesostructured composites, 1,12 and some inorganic salts are often needed to promote the formation of ordered mesostructure.…”