Young Gul Kim

Mixed alcohol synthesis from carbon monoxide and dihydrogen over potassium-promoted molybdenum carbide catalysts

Abstract Unsupported molybdenum carbides, β-Mo 2 C and α-MoC 1-x , promoted by K 2 CO 3 were studied as catalysts for carbon monoxide-hydrogen reactions at 573 K and 8.0 MPa. Unpromoted molybdenum carbides produce mainly hydrocarbons of C 1 -C 12 under these conditions. Addition of K 2 CO 3 as a promoter, however, greatly enhances the selectivity to alcohols composed of linear C 1 -C 7 . Compared with better known alkali-promoted MoS 2 catalysts, carbide catalysts show higher selectivities of C 2 -C 7 alcohols. The carbon number distributions of both hydrocarbon and alcohol are consistent with the Schulz-Flory equation. Unlike MoS 2 catalysts, the addition of hydrogen sulfide in the feed over molybdenum carbide catalysts causes a gradual decrease in activity and selectivity for alcohols with reaction time.

Preparation and benzene hydrogenation activity of supported molybdenum carbide catalysts

Alumina-supported molybdenum carbide catalysts have been prepared from MoO{sub 3}/Al{sub 2}O{sub 3} by (1) reduction with H{sub 2} followed by carburization, (2) direct carburization with CH{sub 4}/H{sub 2}, and (3) nitriding with NH{sub 3} followed by carburization. The temperature required for the complete reduction of MoO{sub 3}/Al{sub 2}O{sub 3} depended strongly on the reductant employed. Temperature-programmed reduction coupled with on-line mass spectrometry and X-ray diffraction revealed reactions involved in the reduction and carburization of MoO{sub 3}. The supported molybdenum carbide catalysts exhibited high catalytic activity in benzene hydrogenation comparable to those of Pt or Ru. Complete reduction of molybdenum was essential for the high activity. Metallic molybdenum was much less active and less stable than its carbides, probably due to too strong adsorption of benzene.

Methyl formate as a new building block in C1 chemistry

Abstract Methyl formate has been proposed as a building block molecule in C1 chemistry. This paper examines the potential of this concept by reviewing the processes of synthesis of the molecule and the chemical reactions that it undergoes. Methyl formate can be produced by a variety of routes from a number of feedstocks. The reaction between methanol and carbon monoxide is an efficient process, used commercially. Combination of an efficient synthesis of methyl formate and its facile decomposition allows the molecule to be used as a means for separation, storage and transport of synthesis gas. The number of reactions that convert methyl formate to other chemicals is large. In particular, the synthesis of large volume chemicals such as methanol, acetic acid and ethylene glycol deserves serious consideration. Examples are provided of applications in the chemical and energy industries involving methyl formate. The reactions involved in the synthesis and transformation of methyl formate are mostly catalytic in nature. Many currently known catalytic systems are not efficient to compete with conventional routes involving methanol or synthesis gas. Fundamental research to understand the catalytic chemistry involved is highly desirable in order to improve the performance of the catalytic systems.

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO2 reforming of methane was studied over modified Ni/Al2O3 catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al2O3, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO2 reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation.

Highly donor-doped (110) layered perovskite materials as novel photocatalysts for overall water splitting

Highly donor-doped (110) layered perovskite materials with a generic composition of AmBmO3m+2 (m = 4, 5; A = Ca, Sr, La; B = Nb, Ti) loaded with nickel have been found to be efficient photocatalysts for overall water splitting with quantum yields as high as 23% under UV irradiation.

Role of alkali promoters in K/MoS2 catalysts for CO-H2 reactions

Abstract The effect of alkali promoters on selectivity of CO-H 2 reactions was studied for potassium-promoted MoS 2 employing different potassium salts and pretreatment conditions (oxidized vs. fresh samples). Promoters assisted either chain growth of hydrocarbon products or alcohol formation. A good correlation was observed between p K a of the conjugate acid of each promoter and its spacetime yield of alcohol formation. Alcohol selective promoters such as K 2 CO 3 , KOH and K 2 S readily removed their counter anions under the reaction conditions to form a new potassium complex and spread themselves uniformly over MoS 2 . This complex appears to serve as an active site which adsorbs carbon monoxide molecularly and, at the same time, cover the majority of the MoS 2 surface which is responsible for dissociative carbon monoxide adsorption and hydrogenation. Promoters for chain growth such as K 2 SO 4 and KCl maintained their initial chemical states throughout the reactions and showed highly nonuniform lateral distributions. Thus, the promoters have a limited coverage over MoS 2 , yet modify the electronic state of MoS 2 which interacts directly with carbon monoxide. Exposure of K 2 CO 3 - or KOH-promoted MoS 2 to atmosphere for an extended period oxidized the catalyst and caused segregation of potassium into the bulk of MoS 2 Thus, the most of MoS 2 surface is now exposed, yet modified by potassium located in the subsurface region of MoS 2 . These modified catalysts promoted hydrocarbon chain growth without forming alcohols. The results demonstrate that the distribution of promoter is one of the primary factors determining its role in catalytic CO-H 2 reactions.

Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for no reduction by NH3

Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for NO reduction by NH3 was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO2 feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH4)2SO4 and/or (NH4)HSO4 from the results of TGA and ion-chromatography measurement.

Preparation and characterization of magnesia-supported chromium catalysts for the fluorination of 1,1,1-trifluoro-2-chloroethane (HCFC-133a)

Abstract Chromium oxides dispersed on various supports by precipitation method were tested for the catalytic fluorination of HCFC-133a to HFC-134a. Catalytic activity decreased in the order of MgO>Al 2 O 3 >MgF 2 >TiO 2 >ZrO 2 . The most active Cr/MgO, when properly activated and pre-fluorinated before the reaction, shows superior activity to other catalysts that have been reported so far. Isolated (monomeric) Cr(VI) species that was formed during an optimized thermal activation were changed into fluoride (Cr x F y ) and oxyfluoride (Cr x O y F z ) form of monomeric and oligomeric Cr species during the pre-fluorination with HF, the latter of which are believed to be active sites for the reaction. High pre-fluorination temperature accelerates the formation of crystalline Cr 2 O 3 due to the formation of crystalline MgF 2 from MgO which anchors the isolated Cr(VI).

Regioselective synthesis of ibuprofen via the palladium complex catalyzed hydrocarboxylation of 1-(4-isobutylphenyl) ethanol

Abstract The synthesis of 2-(4-isobutylphenyl) propionic acid (ibuprofen) by the hydrocarboxylation of 1-(4-isobutylphenyl) ethanol with carbon monoxide and water has been studied in the presence of PdCl 2 –PPh 3 –HCl catalyst system. An almost regiospecific synthesis has been achieved under moderate reaction temperatures and pressures. In this reaction system, the liquid phases comprised of an acid-stable organic solvent and an acidic aqueous phase, and the miscibility between two phases were important for efficient hydrocarboxylation. The rate of reaction and the selectivity to the desired branched acid depended strongly upon the pressure of carbon monoxide, the ratio of phosphine ligand to palladium, the concentration of hydrochloric acid, and the nature of halide ion used.

ROOM-TEMPERATURE OXIDATION OF K2CO3/MOS2 CATALYSTS AND ITS EFFECTS ON ALCOHOL SYNTHESIS FROM CO AND H2

Potassium-promoted MoS2 is used as a catalyst for mixed alcohol synthesis from CO and H2. This study investigates the room-temperature oxidation of the catalyst and its effect on the surface structure and catalytic activity in alcohol synthesis at 573 K and 1.5 MPa. Catalysts were stored in the atmosphere or in a vacuum oven for several weeks. The characterization of catalyst was performed using XRD, XPS, FT-IR, and TGA/DTA methods. The XPS data of K2CO3/MoS2 stored in the atmosphere for extended periods indicated the oxidations of Mo(IV) (as sulfide) to Mo(VI) (as oxide) as well as S2− (as sulfide) to S6+ (as sulfate) on the MoS2 surface. The IR results showed that sulfate species first produced by oxidation had Td symmetry, which was further transformed into C2ν (bidentate) upon a prolonged storage. The sulfate species formed on the catalyst surface were stable until they were decomposed above 1000 K. The oxidized K2CO3/MoS2 catalyst showed enhanced catalytic activity and high selectivity to C2+ hydrocarbons, rather than forming alcohols as did fresh K2CO3/MoS2. These modified catalytic properties were similar to those of fresh K2SO4/MoS2.