Ordered mesoporous materials in catalysis

3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

/pdf/metal-catalyzed-epoxidations-of-alkenes-with-hydrogen-3kxbglgruw.pdf

Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Oxidative dehydrogenation of ethane and propane : How far from commercial implementation?

Selective catalytic reduction (SCR) of NO with NH3 over manganese substituted iron titanate catalysts was fully studied. The low temperature SCR activity was greatly enhanced when partial Fe was substituted by Mn, although the N-2 selectivity showed some decrease to a certain extent. The Mn substitution amounts showed obvious influence on the catalyst structure, redox behavior and NH3/NOx adsorption ability of the catalysts. Among FeaMn1-aTiOx (a = 1, 0.75, 0.5, 0.2, 0) serial catalysts, Fe0.5Mn0.5TiOx with the molar ratio of Fe:Mn = 1: 1 showed the highest SCR activity, because the interaction of iron, manganese and titanium species in this catalyst led to the largest surface area and the highest porosity, the severest structural distortion and most appropriate structural disorder, the enhanced oxidative ability of manganese species, the highest mobility of lattice oxygen, the proper ratio of Bronsted acid sites and Lewis acid sites together with the enhanced NOx adsorption capacity. (C) 2009 Elsevier B.V. All rights reserved.

Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH3

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Single-Atom Catalysts across the Periodic Table.

Characterizations of iron-containing MCM-41 and its catalytic properties in epoxidation of styrene with hydrogen peroxide

Vanadium-Containing MCM-41 for Partial Oxidation of Lower Alkanes

Mn-MCM-41 is found to be the most effective heterogeneous catalyst for the epoxidation of styrene with tert-butyl hydroperoxide (TBHP) among several metal ion-containing mesoporous molecular sieves including Mn-, V-, Cr-, Fe-, and Mo-MCM-41. ESR, XANES, diffuse reflectance UV–VIS, UV–Raman and XPS are used to characterize the Mn-MCM-41 synthesized by both direct hydrothermal (DHT) and template ion exchange (TIE) methods. The results suggest that Mn2+ and Mn3+ coexist in the Mn-MCM-41 samples synthesized by both methods and a large part of manganese atoms could be incorporated into the framework of MCM-41 obtained by the DHT method. The oxidation of either styrene or stilbene with TBHP as the oxidant over the Mn-MCM-41 produces corresponding epoxide as the main product; the reaction probably proceeds through a radical intermediate. The TIE catalyst shows higher activity, while the DHT catalyst gives higher TBHP efficiency for the epoxidation reactions.

Manganese-containing MCM-41 for epoxidation of styrene and stilbene

Cr-MCM-41 synthesized by both direct hydrothermal (DHT) and template-ion exchange (TIE) methods is studied for dehydrogenation of lower alkanes including C 2 H 6 , C 3 H 8 and i-C 4 H 10 with CO 2 . Both methods lead to Cr species highly dispersed on the wall surface of MCM-41 and exhibited similar catalytic behaviors. Selectivity higher than 90% to each alkene has been achieved, and the presence of CO 2 enhances the conversion of alkane.

Cr-MCM-41 for selective dehydrogenation of lower alkanes with carbon dioxide

Fe-MCM-41 has been characterized in detail and studied for epoxidation of alkenes with H 2 O 2 . UV-vis, ESR, Fe K-edge XAFS and UV-Raman spectroscopic studies suggest that iron in Fe-MCM-41 is highly dispersed and mainly incorporated into the framework of MCM-41. Fe-MCM-41 is effective for epoxidation of alkenes including styrene, cyclohexene and many other cyclic alkenes with H 2 O 2 . The tetrahedrally coordinated iron sites in the framework of MCM-41 are probably responsible for the epoxidation reactions.

Qinghong Zhang

Papers

Characterizations of iron-containing MCM-41 and its catalytic properties in epoxidation of styrene with hydrogen peroxide

Vanadium-Containing MCM-41 for Partial Oxidation of Lower Alkanes

Manganese-containing MCM-41 for epoxidation of styrene and stilbene

Cr-MCM-41 for selective dehydrogenation of lower alkanes with carbon dioxide

Fe-MCM-41 catalyzed epoxidation of alkenes with hydrogen peroxide