Won Yong Kim

Aqueous‐Solution Route to Zinc Telluride Films for Application to CO2 Reduction

As a photocathode for CO2 reduction, zinc-blende zinc telluride (ZnTe) was directly formed on a Zn/ZnO nanowire substrate by a simple dissolution-recrystallization mechanism without any surfactant. With the most negative conduction-band edge among p-type semiconductors, this new photocatalyst showed efficient and stable CO formation in photoelectrochemical CO2 reduction at -0.2--0.7 V versus RHE without a sacrificial reagent.

Catalytic CO2 hydrogenation to formic acid over carbon nanotube-graphene supported PdNi alloy catalysts

Pure formic acid was successfully produced via CO2 hydrogenation for the first time over a heterogeneous catalyst of PdNi alloy on a carbon nanotube-graphene (CNT-GR) support in water as an eco-friendly solvent without a base additive. The highest formic acid yield obtained was 1.92 mmol with a turnover number of 6.4 and a turnover frequency of 1.2 × 10−4 s−1 under mild reaction conditions of 40 °C and 50 bar. Alloying Pd with Ni brought a significant enhancement in catalytic activity compared to the monometallic Pd catalyst. In addition, the CNT-GR composite as a catalytic support improved the dispersion of Pd–Ni alloy particles, which exhibited good stability under the reaction conditions.

Selective Formation of Hägg Iron Carbide with g‐C3N4 as a Sacrificial Support for Highly Active Fischer–Tropsch Synthesis

The Fischer–Tropsch synthesis (FTS) is a feasible pathway to chemicals and fuels from underutilized resources like coal, natural gas, biomass, and shale gas, instead of the current petroleum‐based production. Owing to its high activity and low price, the iron‐based catalysts are widely used in FTS, yet catalysts with higher activity and better selectivity should be developed for widespread applications. Herein, we report a unique strategy to synthesize an efficient iron catalyst for FTS by applying a graphitic carbon nitride (g‐C3N4) as a sacrificial support. The iron catalyst on g‐C3N4 is effectively reduced to a state that is rapidly and selectively converted to highly crystalline and pure Hägg carbide (χ‐Fe5C2) phase during the FTS reaction. The obtained catalyst exhibits outstanding CO conversion, and high selectivity for C5+ products, outperforming most of the recently reported carbon‐based iron catalysts.

Coke tolerance of Ni/Al2O3 nanosheet catalyst for dry reforming of methane

In the dry reforming of methane with CO2, coke formation in the catalyst during the reaction is the most serious problem. As a coke resistant reforming catalyst, Ni/Al2O3 nanosheets were synthesized by a solvothermal method. The synthesized nanosheet catalysts demonstrated highly stable methane conversion, although the amount of deposited carbon was similar to that in Ni/Al2O3 with a random morphology that deactivated rapidly. The critical effect of nanosheet morphology has been demonstrated on the coke tolerance of the nickel-based dry reforming catalyst.

Isomorphic Ti substitution into SBA-15 without Ti loss and with lower TiO2 segregation.

A convenient method has been discovered to incorporate Ti atoms isomorphically into a SBA-15 lattice without Ti loss. By hydrolysis of a Ti precursor near neutral pH instead of conventional acidic conditions, Ti loss was almost eliminated and its segregation to form TiO2 particles was suppressed while the mesoporous structure remained intact.

Highly Active and Coke-Tolerant Hierarchical Mordenite Catalysts Synthesized by Recrystallization for the Isopropylation of Naphthalene

In the isopropylation of naphthalene for the production of 2,6‐naphthalenedicarboxylate, the monomer of polyethylene naphthalate plastic, a shape‐selective mordenite (MOR) zeolite catalyst provides the best selectivity for the desired 2,6‐diisopropylnaphthalene. However, the small pore size of the zeolite limits the naphthalene conversion and lowers the stability because of pore‐mouth blocking by coke. We discovered that these problems could be mitigated by synthesizing a micro‐meso hierarchical pore structure in the MOR zeolite by the recrystallization of MOR with cetyltrimethylammonium bromide as a mesopore‐forming surfactant. The recrystallized catalysts allow the facile diffusion of bulky molecules through connected meso‐ and micropores to and from active catalytic sites located in the small MOR pores. Relative to microporous MOR, the hierarchical MOR catalyst demonstrated a greatly enhanced activity, stability, and coke tolerance, and the intrinsic high shape selectivity of MOR for 2,6‐diisopropylnaphthalene was maintained. Mild desilication enlarged the pore volume and formed additional acid sites to increase the activity further.

Ultrapermeable Nickel–Cobalt–Manganese/Alumina Inverse Opal as a Coke‐Tolerant and Pressure‐Drop‐Free Catalyst for the Dry Reforming of Methane

An inverse opal‐structured Ni‐Co‐Mn/Al2O3 catalyst with ultrahigh permeability was prepared by a sol–gel method templated by poly(methyl methacrylate) opal‐structured nanospheres. This catalyst exhibited excellent coke tolerance and a negligible reactor pressure drop in the dry reforming of methane. The highly permeable, unique macroporous structure allowed facile mass transport, which not only reduced the amount of coke deposition but also enhanced coke tolerance. Therefore, invariant CO2/CH4 conversions despite substantial coke formation were observed.