Changmook Kim

Synthesis and characterization of mesoporous alumina as a catalyst support for hydrodechlorination of 1,2-dichloropropane: Effect of catalyst preparation method

A mesoporous alumina was synthesized by a posthydrolysis method. The prepared mesoporous alumina was found to have randomly ordered pores, and retained relatively high surface area with narrow pore size distribution centered at ca. 4 nm. Nickel precursors were then supported on the mesoporous alumina by an impregnation (Ni-IMP) and vapor deposition (Ni-VD) method. Several characterizations were carried out in order to investigate physical and chemical properties of mesoporous alumina and supported Ni catalysts. TPR, XPS, and UV-DRS measurements revealed that the Ni-IMP catalyst retained much more amounts of surface nickel aluminate-like species than the Ni-VD sample. TPD experiments also showed that nickel aluminate species affected the adsorption amounts of reactant (1,2-dichloropropane). In the hydrodechlorination of 1,2-dichloropropane (DCPA), DCPA conversion over the Ni-VD catalyst was about two times higher than that over the Ni-IMP catalyst at 300 °C. It is probably due to the fact that the Ni-VD catalyst, which had low contents of nickel aluminate species compared to the Ni-IMP catalyst, exhibited higher degree of reduction than the Ni-IMP catalyst at pretreatment conditions. The difference in DCPA conversion between two catalysts was closely related to the degree of reduction of nickel species and the amounts of adsorption of DCPA onto the catalyst as well.

A novel method for synthesis of a Ni/Al2o3 catalyst with a mesoporous structure using stearic acid salts

Nickel stearate was used as a chemical template and metal source for the easy-and-fast preparation of Ni/Al2O3 catalyst with a mesoporous structure. Ni-Nx and Ni-Hx were prepared using an NH4OH-treated precipitate and a HCl-treated solution as the chemical template, respectively, and these materials show only the effect of the chemical template, a regular pore size distribution. Ni-Nx with both a developed framework and textural porosity show a larger surface area and pore volume but a less irregular pore structure than Ni-Hx which shows a well-developed framework porosity. The 27Al NMR MAS analysis showed that nickel oxide supported on active alumina allows Ni2+ ions to diffuse into the surface lattice vacancies of the alumina spinel structure. Such a migration of metal ions may be limited to the first few layers of the supports, but leads to the production of hard-to-reduce metal oxide (i.e. a high metal-to-support interaction). Ni-Nx was also found to have a more dispersed nickel particle configuration than Ni-Hx after reduction.

Synthesis of mesoporous γ-aluminas of controlled pore properties using alkyl carboxylate assisted method

Abstract Mesoporous γ-alumina (MA) was prepared by alkyl carboxylate assisted method. Pore properties of MAs could be controlled by carbon tail length of template, the molar ratio of sec-butanol to isooctane or water to aluminum precursor, and calcination conditions. The crystalline phase of MA after calcinations was γ-AI 2 O 3 . The pore size of MAs decreased from 7.7 nm to 3.5 nm with the decrease in the ratio of water to aluminium ion, while the pore uniformity was enhanced. Isooctane as a co-solvent acted as an expander of the pores. In addition, as increasing the molar ratio of sec-butanol to isooctane, pore size increased from 2.3 nm to 3.5 nm and both pore uniformity and framework porosity was improved.

Comparison of Mesoporous Aluminas Synthesized using Stearic Acid and Its Salts

Mesoporous aluminas, X-MAs (X=Na, Mg, and Ni) were prepared using stearic acid and its salts as templates. Sodium stearate, which is more soluble than stearic acid, was an effective template for preparing Na-MA. The characteristics of Mg-MA prepared using cost-effective template (magnesium stearate) were similar to those for an MA prepared using stearic acid. Mg ions were easily exchanged with Ni ion by treatment with an acid or base. Thus, nickel incorporated alumina (Ni-MA) could be directly prepared using nickel stearate, which was acting as a chemical template and a metal source. The MA and X-MAs had a similar pore size (3.6 nm), a narrow pore size distribution (DFWHM∼1 nm), and a γ-alumina phase. In addition, bimetallic Ni-MAn catalysts were prepared and applied to the partial oxidation methane as a potential application.

Synthesis of mesoporous alumina by using a cost-effective template

A salt of stearic acid, i.e., magnesium stearate [(C17H35COO)2Mg], can be used as a chemical template for the formation of mesoporous alumina, and is a less expensive reagent than stearic acid. Mesoporous alumina prepared using this cost-effective surfactant shows similar pore properties with respect to pore size (3.5 nm) and surface area (above 300 m2Vg) to that prepared using stearic acid. In addition, textural porosity, arising from non-crystalline intraaggregate voids and spaces, was effectively removed by the addition of magnesium nitrate. The entire transformation from aluminum hydroxide to active alumina was performed at 550 °C, and the crystallinity of the product was confirmed by powder XRD analysis.27A1 MAS NMR result shows the phase of mesoporous alumina is the γ-alumina form.

Response to Comment on “Arsenic Removal Using Mesoporous Alumina Prepared via a Templating Method”

The health threat of arsenic is well-known, and the U.S. EPA recommends the maximum contaminant level to be 0.01 ppm or less for arsenic in drinking water. Therefore, advanced treatment processes are needed for finished water to meet the required regulations. Adsorption is considered to be a less expensive procedure that is safer to handle than precipitation, ion exchange, and membrane filtration. Activated alumina (AA) is the most commonly used adsorbent for the removal of arsenic from aqueous solutions. However, conventional porous solids including AA have ill-defined pore structures and, typically, low adsorption capacities and act in a kinetically slow manner. An ideal adsorbent should have uniformly accessible pores, an interlinked pore system, a high surface area, and physical and/or chemical stability. To meet this requirement, mesoprous alumina (MA) with a wide surface area (307 m2/g) and uniform pore size (3.5 nm) was prepared, and a spongelike interlinked pore system was developed through a post-hydrolysis method. The resulting MA was insoluble and stable within the range of pH 3-7. The maximum uptake of As(V) by MA was found to be 7 times higher [121 mg of As(V)/g and 47 mg of As(III)/ g] than that of conventional AA, and the kinetics of adsorption were also rapid with complete adsorption in less than 5 h as compared to the conventional AA (about 2 d to reach half of the equilibrium value). A desorption study using sodium hydroxide solutions (0.01-1 M) was conducted, and 0.05 M NaOH was found to be the most suitable desorption agent. More than 85% of the arsenic adsorbed to the MA was desorbed in less than 1 h. Several other activated aluminas with different pore properties were also tested. The results show that the surface area of the adsorbents does not greatly influence on the adsorption capacity. In fact, the key factor is a uniform pore size and an interlinked pore system. These studies show that MA with a wide surface area, uniform pore size, and interlinked pore system can be used as an efficient adsorbent for the removal of arsenic.