15 research outputs found
An Overview of Recent Development in Composite Catalysts from Porous Materials for Various Reactions and Processes
Catalysts are important to the chemical industry and environmental remediation due to their effective conversion of one chemical into another. Among them, composite catalysts have attracted continuous attention during the past decades. Nowadays, composite catalysts are being used more and more to meet the practical catalytic performance requirements in the chemical industry of high activity, high selectivity and good stability. In this paper, we reviewed our recent work on development of composite catalysts, mainly focusing on the composite catalysts obtained from porous materials such as zeolites, mesoporous materials, carbon nanotubes (CNT), etc. Six types of porous composite catalysts are discussed, including amorphous oxide modified zeolite composite catalysts, zeolite composites prepared by co-crystallization or overgrowth, hierarchical porous catalysts, host-guest porous composites, inorganic and organic mesoporous composite catalysts, and polymer/CNT composite catalysts
Water-Involved Methane Selective Catalytic Oxidation by Dioxygen over Copper-Zeolites
The selective oxidation of methane to methanol is a dream reaction of
direct methane functionalization, which remains a key challenge in catalysis
and a hot issue of controversy. Herein, we report the water-involved methane
selective catalytic oxidation by dioxygen over copper-zeolites. At 573 K, a
state-of-the-art methanol space-time yield of 543 mmol/molCu/h with
methanol selectivity of 91 % is achieved with Cu-CHA catalyst. Temperature-programmed
surface reactions with isotope labelling determine water as the dominating oxygen
and hydrogen source of hydroxyl in methanol while dioxygen participates in the
reaction through reducing to water. Spectroscopic analyses reveal the fast redox cycle of Cu2+-Cu+-Cu2+ during methane selective oxidation, which is closely related to the high catalytic activity of Cu-CHA. Density functional theory calculations
suggest that both CuOH monomer and dimer in Cu-CHA can catalyze the selective
oxidation of methane to methanol with Cu-OOH as the key reaction intermediate, and meanwhile, various copper sites undergo
interconversion under reaction conditions.</p
Acetylene-Selective Hydrogenation Catalyzed by Cationic Confined in Zeolite
The selective hydrogenation of alkynes to alkenes is an important type of organic transformation with large-scale industrial applications. This transformation requires efficient catalysts with precise selectivity control, and palladium-based metallic catalysts are currently employed. Here we show that four-coordinated cationic nickel(II) confined in zeolite can efficiently catalyze the selective hydrogenation of acetylene to ethylene, a key process for trace acetylene removal prior to the polymerization process. Under optimized conditions, 100% acetylene conversion and an ethylene selectivity up to 97% are simultaneously achieved. This catalyst system also exhibits good stability and recyclability for potential applications. Spectroscopy investigations and density functional theory calculations reveal the heterolytic dissociation of hydrogen molecules and the importance of hydride and protons in the selective hydrogenation of acetylene to ethylene. This work provides an efficient strategy toward active and selective zeolite catalysts by utilizing the local electrostatic field within the zeolite confined space for small-molecule activation and by linking heterogeneous and homogeneous catalysis
Affecting the Formation of the Micro‐structure and Meso/macro‐structure of SAPO‐34 zeolite by Amphipathic Molecules
Hexadecylphosphate-Functionalized Iron Oxide Nanoparticles: Mild Oxidation of Benzyl C–H Bonds Exclusive to Carbonyls by Molecular Oxygen
We
report here a specially designed catalytic system consisting
of hexadecylphosphate-functionalized iron oxide nanoparticles
in oil/water biphasic emulsion. The iron oxide nanoparticles act as
catalytic centers and the surface-bonded hexadecylphosphates
as peripheral units which tune the activity of iron oxide and the
access of reactants to the catalytic centers. The catalytic system
is highly effective to oxidize the benzyl C–H bonds in a series
of compounds to carbonyls exclusively by molecular oxygen under mild
conditions. The catalytic process, green and low cost, offers a novel
concept to design highly effective catalysts with nanoparticles as
active centers and surface-bonded organic phosphates as accelerants
for oxidation reactions
Understanding the Early Stages of the Methanol-to-Olefin Conversion on H‑SAPO-34
Little
is known on the early stages of the methanol-to-olefin (MTO)
conversion over H-SAPO-34, before the steady-state with highly active
polymethylbenzenium cations as most important intermediates
is reached. In this work, the formation and evolution of carbenium
ions during the early stages of the MTO conversion on a H-SAPO-34
model catalyst were clarified via <sup>1</sup>H MAS NMR and <sup>13</sup>C MAS NMR. Several initial species (i.e., three-ring compounds, dienes,
polymethylcyclopentenyl, and polymethylcyclohexenyl cations)
were, for the first time, directly verified during the MTO conversion.
Their detailed evolution network was established from theoretical
calculations. On the basis of these results, an olefin-based catalytic
cycle is proposed to be the primary reaction pathway during the early
stages of the MTO reaction over H-SAPO-34. After that, an aromatic-based
cycle may be involved in the MTO conversion for long times on stream