Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH.

Optimized photocatalytic conversion of CO2 requires new potent catalysts that can absorb visible light. The photocatalytic reduction of CO2 using rhenium(i) has been demonstrated but suffers from low turnover. Herein, we describe a [Re(CO)3(1-(1,10)phenanthroline-5-(4-nitro-naphthalimide))Cl] photocatalyst, which when combined with the sacrificial donor 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, results in selective production of formic acid and a high turnover number of 533 and turnover frequency of 356 h-1. Single-crystal X-ray diffraction and DFT studies are also discussed.

ZSM-5 decrystallization and dealumination in hot liquid water.

Zeolites have recently attracted attention for upgrading renewable resources in the presence of liquid water phases; however, the stability of zeolites in the presence of liquid-phase water is not completely understood. Accordingly, the stability of the ZSM-5 framework and its acid sites was studied in the presence of water at temperatures ranging from 250 to 450 °C and at pressures sufficient to maintain a liquid or liquid-like state (25 MPa). Treated samples were analyzed for framework degradation and Al content and coordination using a variety of complementary techniques, including X-ray diffraction, electron microscopy, N2 sorption, 27Al and 29Si NMR spectroscopy, and several different types of infrared spectroscopy. These analyses indicate that the ZSM-5 framework retains >80% crystallinity at all conditions, and that 300-400 °C are the most aggressive. Decrystallization appears to initiate primarily at crystal surfaces and share many characteristics in common with alkali promoted desilication. Liquid water treatment promotes ZSM-5 dealumination, following a mechanism analogous to that observed under steaming conditions: initiation by Al-O hydrolysis, Al migration to the surface, and finally deposition as extra framework Al or possibly complete dissolution under some conditions. As with the framework, dealumination is most aggressive at 300-400 °C. Several models were evaluated to capture the non-Arrhenius effect of temperature on decrystallization and dealumination, the most successful of which included temperature dependent values of the water auto-ionization constant. These results can help interpretation of previous studies on ZSM-5 catalysis in hot liquid water and suggest future approaches to extend catalyst lifetime.

SAPO-34/5A Zeolite Bead Catalysts for Furan Production from Xylose and Glucose.

SAPO-34 zeolite crystals were grown on zeolite 5A beads, characterized, and then used to produce furfural from xylose and 5-hydroxymethylfurfural (HMF) from glucose. The SAPO-34/5A bead catalysts resulted in moderate furfural and HMF yields of 45% from xylose and 20% from glucose (463 K; 3 h) and were easier to recover than the SAPO-34 powder catalyst. At 463 K, the SAPO-34/5A beads were more selective than 0.02 M sulfuric acid for producing HMF and, unlike the sulfuric acid system, no levulinic acid was formed. The SAPO-34/5A bead catalysts had no significant loss in activity after three rounds of recycle when water washed or heated overnight between reactions; however, the heat-treated beads did show signs of thermal stress after the second reuse. The SAPO-34/5A bead catalysts show promise for dehydration reactions to produce furfural and HMF from xylose and glucose, respectively, and tailoring the catalyst and the support bead could lead to even higher selectivities and yields.

γ-Valerolactone ring-opening and decarboxylation over SiO2/Al2O3 in the presence of water.

γ-Valerolactone (GVL) has been identified as a promising, sustainable platform molecule that can be produced from lignocellulosic biomass. The chemical flexibility of GVL has allowed the development of a variety of processes to prepare renewable fuels and chemicals. In the present work involving a combination of computational and experimental studies, we explore the factors governing the ring-opening of GVL to produce pentenoic acid isomers, as well as their subsequent decarboxylation over acid catalysts or hydrogenation over metal catalysts. The ring-opening of GVL has shown to be a reversible reaction, while both the decarboxylation and hydrogenation reactions are irreversible and kinetically controlled under the conditions studied (temperatures from about 500 to 650 K). The most significant contributor to lactone reactivity toward ring-opening is the size of the ring, with γ- lactones being more stable and less readily opened than δ- and ε-analogues. We have observed that the presence of either a C═C double bond or a lactone (which opens to form a C═C double bond) is necessary for appreciable rates of decarboxylation to occur. Olefinic acids exhibit higher rates of decarboxylation than the corresponding lactones, suggesting that the decarboxylation of alkene acids provides a lower energy pathway to olefin production than the direct decarboxylation of lactones. We observe lower rates of decarboxylation as the chain length of alkene acids increases; however, acrylic acid (3-carbon atoms) does not undergo decarboxylation at the conditions tested. These observations suggest that particular double bond configurations yield the highest rates of decarboxylation. Specifically, we suggest that the formation of a secondary carbenium ion in the ß position leads to high reactivity for decarboxylation. Such an intermediate can be formed from 2- or 3-alkene acids which have at least four carbon atoms.

Integrated catalytic conversion of gamma-valerolactone to liquid alkenes for transportation fuels.

Efficient synthesis of renewable fuels remains a challenging and important line of research. We report a strategy by which aqueous solutions of gamma-valerolactone (GVL), produced from biomass-derived carbohydrates, can be converted to liquid alkenes in the molecular weight range appropriate for transportation fuels by an integrated catalytic system that does not require an external source of hydrogen. The GVL feed undergoes decarboxylation at elevated pressures (e.g., 36 bar) over a silica/alumina catalyst to produce a gas stream composed of equimolar amounts of butene and carbon dioxide. This stream is fed directly to an oligomerization reactor containing an acid catalyst (e.g., H ZSM-5, Amberlyst-70), which couples butene monomers to form condensable alkenes with molecular weights that can be targeted for gasoline and/or jet fuel applications. The effluent gaseous stream of CO2 at elevated pressure can potentially be captured and then treated or sequestered to mitigate greenhouse gas emissions from the process.