Search

Ethylene oligomerization with controlled chain lengthening over the shape-selective HZSM-5 catalyst provides alternative technologies for the production of C3+light olefins under the current circumstances of shifting hydrocarbon feedstocks from naphtha to ethane. Here, by tuning the MFI framework Alfsite to either isolated or in close proximity, we investigated the influence of the Alfproximity on the kinetics and mechanisms of ethylene oligomerization. We demonstrate that the HZSM-5 catalyst with a high concentration of Alfin close proximity (AlHProx) shows higher activity. The reaction rate of AlHProxis up to 14-fold that of AlIso(HZSM-5 with isolated Alf). Steady-state kinetic studies showed that the activation energy for AlIso(104.8 kJ mol−1) was lower than that for AlHProx(144.5 kJ mol−1). In addition, the kinetic compensation effect with the isokinetic point (Tiso) at 177 °C and Rateisoat 0.015 μmol g−1s−1was identified. Further reaction transient analysis suggested that the dual-cycle hydrocarbon-pool (HP) mechanism was involved. Unlike the steady state, the transient state favors the formation of alkanes and aromatics, indicating the establishment of cyclic carbocations through oligomerization, cyclization, and hydride transfer. The early-stage (HP build-up) behavior seemed to be independent of the Alfproximity, but the back-transient (HP clean-up) suggested decrease in the aromatic cycle over the AlHProxsample.

Crude oil is very difficult to refine because of its large and very heavy oil molecules. The increased external surface areas of the engineered catalysts used in FCC contribute to promoting the preliminary cracking of heavy or extra-heavy oil molecules. Core–shell zeolites with a commercial Y zeolite core and a polycrystalline shell composed of loosely aggregated Y nanocrystals are designed and synthesized. Compared to a commercial Y zeolite catalyst, the as-synthesized core–shell Y zeolite with a high percentage of silicon in the shell exhibits excellent catalytic performance during the catalytic cracking of tri-isopropylbenzene, n-octane, and their physical mixture because of the increased external surface area and high hydrothermal stability. The results verify that large reactants can undergo a hierarchical cracking process over the as-prepared core–shell Y zeolite catalyst: the reactants can be pre-cracked on the accessible external surfaces and the pre-cracked products can be further deeply cracked by the strong acid centers in the confined microporous channels.

Three Pd/CeO2catalysts are synthesized by reduction-deposition and an impregnation method (IMP) to clarify how the chemical state of Pd influences the catalytic performance for CH4combustion. The results show that Pd/CeO2(HHA), using hydrazine hydrate as a reductant, shows much higher catalytic activity and stability for CH4combustion than Pd/CeO2(FA), using formaldehyde as a reductant, and Pd/CeO2(IMP). The results of our comprehensive characterization reveal that there are two different chemical states of Pd species on Pd/CeO2: Pd2+in the form of PdO particles and Pdδ+(2 < δ≤ 4) in the form of PdxCe1−xO2, and the latter is mainly induced by the Pd species entering the lattice of CeO2, which acts as a transfer channel of active oxygen species from the CeO2lattice to active Pd species. The activity of Pd/CeO2directly correlates to the surface concentrations of PdO and adsorbed oxygen. An increase in the amount of PdxCe1−xO2would thicken the transition layer and decrease the replenishment rate of oxygen vacancies through diffusion of lattice oxygen. Meanwhile, the existence of more PdxCe1−xO2could promote the capture of produced CO2on the CeO2around Pd species and decrease the catalytic activity.

A facile fabrication approach for metal oxide/C materials with a hierarchical pore structure on different length scales is proposed. The material is synthesized from inorganic/organic metal oxo clusters as molecular precursors and processed using a dual-template method followed by heat treatment. TiO2and ZrO2were used as two examples of metal oxide materials and their corresponding carbon-based composites showed superior photocatalytic activity in methylene blue degradation compared with the control samples. This work demonstrates a novel approach for processing metal oxide-based photocatalysts with enhanced reactivity that is broadly applicable to the design of complex functional metal oxide composites with high electrochemical performance for energy applications.

Ru/13X zeolite catalysts containing 0.6, 2 and 5.7% Ru prepared by reduction or decomposition of the hexammine complex are active and stable for n-butane hydrogenolysis between 400 and 460 K, and show similar activation energies (150–160 kJ mol−1) and orders of reaction (−1.5 to −2 in H2; 0.5–0.65 in n-butane); product selectivities show weak dependence on temperature and H2pressure, with preference for terminal bond scission. Oxidising either the decomposed or the reduced catalysts gave a marked increase in activity, a lower activation energy (120–130 kJ mol−1), higher orders of reaction in H2(∼−0.9), lower orders in n-butane (∼0.2) and product selectivities that showed greater change with temperature and H2pressure; terminal bond scission was >90%. The change in character with oxidation was attributed to weaker H2chemisorption and a higher concentration of partially dehydrogenated C4species; the active phase may consist of very small particles of RuO2confined within the supercages of the zeolite.