Organic Reactions: Sections 4.1 – 4.4

Spectroscopic and Computational Study of Cr Oxide Structures and Their Anchoring Sites on ZSM-5 Zeolites

“…Therefore, zeolites with a low concentration of Al (high Si/Al ratios) should have anchoring sites and Cr oxide structures that are similar to those on SiO 2 supports. Our previous Raman spectroscopic studies show that dehydrated Cr/SiO 2 catalysts have mainly isolated Cr oxide species (species with a single Cr atom) with Raman bands at 982 and 1011 cm –1 . − The structure of Cr/SiO 2 catalysts has been extensively studied, − and the dominance of isolated surface Cr species is consistent with multiple characterization studies: for example, with results obtained with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies − and with characterization of a model CrO x /SiO 2 /Si­(110) system with XPS, secondary-ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS) . Our computational study of isolated Cr­(VI) oxide species supported on SiO 2 identified two main types of Cr structures: (1) a dioxo (Si–O−) 2 Cr­(O) 2 structure with a symmetric stretching vibration ν s for the OCrO fragment that matches the experimental Raman band at 982 cm –1 and (2) a mono-oxo (Si–O−) 4 Cr­(O) structure with a stretching vibration ν for the CrO fragment that matches the experimental Raman band at 1011 cm –1 …”

“…Cr catalysts with silica and alumina supports are used in a wide range of industrial applications. For example, Cr/SiO 2 catalysts are used in the production of high-density polyethylene − and Cr/Al 2 O 3 in alkane dehydrogenation. ,,, Zeolite-supported Cr catalysts, specifically Cr/ZSM-5, have been evaluated for multiple applications, such as toluene disproportionation, combustion of volatile and chlorinated organic compounds, − reduction of nitrogen oxides, , styrene selective oxidation to benzaldehyde, photocatalytic partial oxidation of propane to acetone, ethylene ammoxidation, , and oxidative dehydrogenation of ethane with CO 2 . Furthermore, Cr has been used as a promoter for other metals supported on ZSM-5 or physically mixed with ZSM-5: for example, for Mo/ZSM-5 in methane dehydroaromatization, for Zn and Co/ZSM-5 in Fischer–Tropsch synthesis, , and in NO reduction by H 2 …”

Pushing the Limits on Metal–Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation

“…At the low conversions used in these experiments, the selectivity to pxylene is expected to be low, because two methyl shifts would be required before desorption from the active site. The experimental absence of p-xylene in these experiments also rules out direct ortho to para transitions that have been proposed for an intermolecular pathway 66 or from an extremely active catalyst. 67 In the intermolecular mechanism, two reactant molecules disproportionate to yield toluene and trimethylbenzene.…”

Desymmetric Hydrogenation of meso-Dicarboxylic Acids

“…The catalytic chemical routes to the reduction of carboxylic acids and their derivatives by molecular hydrogen, with high atom economy, have become a considerable alternative approach. Heterogeneous hydrogenation is typically carried out under harsh conditions, and the chemo-selectivities among different unsaturated functionalities have impeded the large-scale application of this approach in the production of complex molecules. , Chemical practitioners have still been seeking homogeneous hydrogenation methods to reduce carboxylic acids and derivatives. , From a theoretical perspective, the difficulty of hydrogenation of carboxylic acids lies before that of amides and carbamates, similar to esters. The ability of the CO bond in carboxylic and carbonic acid derivatives to accept a hydride donor is believed in parallel to the order of susceptibility to nucleophilic attack at the carbonyl function. , However, because a majority of successful catalytic systems for hydrogenation of esters and amides were carried out in basic conditions, these cases of transition-metal catalysis tend to fail for carboxylic acids that are deprotonated in the reaction (Figure b).…”