Catalytic routes to transportation fuels utilizing natural gas hydrates

Multiple-Functional Capsule Catalysts: A Tailor-Made Confined Reaction Environment for the Direct Synthesis of Middle Isoparaffins from Syngas

A capsule catalyst for isoparaffin synthesis based on Fischer-Tropsch reaction was designed by coating a H-ZSM-5 membrane onto the surface of the pre-shaped Co/SiO(2) pellet. Morphological and chemical analysis showed that the capsule catalyst had a core-shell structure. A compact, integral shell of H-ZSM-5 crystallized firmly on the Co/SiO(2) substrate without crack. Syngas passed through the zeolite membrane to reach the Co/SiO(2) catalyst to be converted, and all hydrocarbons formed with straight chain structure must enter the zeolite channels to undergo hydrocracking as well as isomerization in this tailor-made confined reaction environment. A narrow, anti-Anderson-Schultz-Flory law product distribution was observed on these capsule catalysts. Contrary to a mechanical mixture of H-ZSM-5 and Co/SiO(2), C(10+) hydrocarbons were suppressed completely on this novel capsule catalyst, and the selectivity of middle isoparaffins was considerably improved. The carbon number distribution of the products depended on the thickness of the zeolite membrane, and it was possible to selectively synthesize specified distillates, such as gasoline-range, or heavier hydrocarbons from syngas directly, by simply adjusting the thickness of the zeolite membrane of the capsule catalyst. This kind of capsule catalysts can be extended to various consecutive reaction systems as the shell and core components are independent catalysts for different reactions. At the same time, shape selectivity and space-confined effects can be expected for the reactant, intermediates and product of the sequential reactions.

Designing a capsule catalyst and its application for direct synthesis of middle isoparaffins

A catalyst in the form of a capsule catalyst was prepared by coating HZSM5 membrane on a preshaped Co/SiO2 catalyst pellet. The capsule catalyst with HZSM5 membrane exhibited excellent selectivity for light hydrocarbon synthesis, especially for isoparaffin synthesis from syngas (CO + H2). Long-chain hydrocarbon formation was totally suppressed by the zeolite membrane. The modification of membrane and core catalyst significantly improved the catalytic properties of these new kinds of capsule catalysts.

Kinetic modeling of homogeneous methanol synthesis catalyzed by base-promoted nickel complexes

Nickel complexes promoted by alkoxide bases can affect facile conversion of synthesis gas into methanol under thermodynamically favorable temperatures. At 100°C, syngas conversion of 99% with turnover frequency of 66 h-1 is reported. The reaction is truly catalytic in Ni as well as in base. A kinetic study of the Ni(CO)4-KOMe catalyst system in 1,2-bis(2-methoxy ethoxy)ethane (triglyme)-MeOH solvent mixture is presented. The kinetic expression includes terms of zero-order in H2 and first-order in CO with syngas of H2-CO stoichiometry of ~2:1 and less than first-order in Ni (0.03-0.10 M), ~third-order in base (2.0-4.75 M), and an exponential dependence on methanol concentration (13.0-23.7 M at 2.0 M base; 15.8-22.6 M at 3.0 M base). The activation energy of 42.2 kJ mol-1 was estimated from the Arrhenius plot of the data between 374 and 393 K. Gas phase IR spectrum at the end of each run showed an intense signature peak at 2060 cm-1 for Ni(CO)4. Process uncertainties to commercialization of this versatile homogenous catalyst system for CO hydrogenation to methanol are discussed.Key words: homogeneous catalysis, syngas conversion, methanol synthesis, alkoxides, carbonyls of nickel.