Piyasan Praserthdam

A Single‐Site Platinum CO Oxidation Catalyst in Zeolite KLTL: Microscopic and Spectroscopic Determination of the Locations of the Platinum Atoms

A stable site-isolated mononuclear platinum catalyst with a well-defined structure is presented. Platinum complexes supported in zeolite KLTL were synthesized from [Pt(NH3)4](NO3)2, oxidized at 633 K, and used to catalyze CO oxidation. IR and X-ray absorption spectra and electron micrographs determine the structures and locations of the platinum complexes in the zeolite pores, demonstrate the platinum-support bonding, and show that the platinum remained site isolated after oxidation and catalysis.

Effect of Cobalt Precursors on the Dispersion of Cobalt on MCM-41

Co/MCM-41 catalysts were prepared using the incipient wetness impregnation technique with aqueous solutions of different cobalt compounds such as cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt acetylacetonate. MCM-41 is known to have a restricted pore structure; however, using organic precursors such as cobalt acetate and cobalt acetylacetonate resulted in very small cobalt oxide particles that could not be detected by XRD even for a cobalt loading as high as 8 wt%. These cobalt particles were small enough to fit into the pores of MCM-41. However, they were found to chemisorb CO in only relatively small amounts and to have low activities for CO hydrogenation—probably due to the formation of cobalt silicates. The use of cobalt chloride resulted in very large cobalt particles/clusters and/or residual Cl--blocking active sites, and, consequently, very small active surface area was measurable. The use of cobalt nitrate resulted in a number of small cobalt particles dispersed throughout MCM-41 and some larger particles located on the external surface of MCM-41. Cobalt nitrate appeared to be the best precursor for preparing high-activity MCM-41-supported cobalt Fischer–Tropsch synthesis catalysts.

The influence of Si-O-Zr bonds on the crystal-growth inhibition of zirconia prepared by the glycothermal method

Abstract SiO 2 -modified ZrO 2 with the Si/Zr ratios of 0.04, 0.08, and 0.15 were prepared by the reaction of zirconium n -propoxide and tetraethyl orthosilicate in 1,4-butanediol. The products were characterized by FT-IR and XRD. The FT-IR spectra exhibit the presence of Si–O–Zr bonds formed during the reaction, indicating a high degree of powder homogeneity. The presence of Si–O–Zr bonds retards the crystal growth upon calcination.

Theoretical study on the synthesis of methyl acetate from methanol and acetic acid in pervaporation membrane reactors: effect of continuous-flow modes

Abstract The synthesis of methyl acetate (MeOAc) from methanol (MeOH) and acetic acid (HOAc) in pervaporation membrane reactors (PVMRs) is discussed in this paper. Three modes of PVMR operation, i.e. semi-batch (SB-PVMR), plug-flow (PF-PVMR) and continuous stirred tank (CS-PVMR) were modeled using the kinetic parameters of the reaction over Amberlyst-15 and permeation parameters for a polyvinyl alcohol (PVA membrane). Both of the reaction and permeation rates are expressed in terms of activities. The PVA membrane shows high separation factors for HOAc and MeOAc but very low for MeOH. The simulation results of SB-PVMR mode show quite good agreement with the experimental results. The study focused on comparing PVMR performances between two modes of continuous-flow operation for various dimensionless parameters, such as Damkohler number ( Da ), the rate ratio ( δ ), the feed composition and the membrane selectivity. Flow characteristic within the reactors arisen from different operation modes affects the reactor performance through its influences on the reaction and permeation rates along the reactor. There are only some ranges of operating conditions where CS-PVMR is superior to PF-PVMR.

Synthesis of thermally stable micro spherical χ-alumina by thermal decomposition of aluminum isopropoxide in mineral oil

Abstract Thermal decomposition of aluminum isopropoxide (AIP) in mineral oil at 250–300 °C over a 2 h duration results in χ-alumina powders having high thermal stability. The mechanism of the process involves the formation of amorphous complex before further decomposition takes place. Phase transformation of the obtained products was also investigated. It was found that χ-alumina synthesized by this method transformed directly to α-alumina at temperature higher than 1000 °C.

Effect of the pretreatment with oxygen and/or oxygen-containing compounds on the catalytic performance of Pd-Ag/Al2O3 for acetylene hydrogenation

Abstract Catalytic performance of Pd-Ag/α-Al 2 O 3 was studied for the selective hydrogenation of acetylene in the presence of excess ethylene. The catalyst activation was undertaken prior to the reaction test by the pretreatment with oxygen and/or oxygen-containing compounds, i.e. O 2 , NO, N 2 O, CO and CO 2 . The enhancement of catalytic performances by the pretreatment was a consequence of an increase in accessible Pd sites responsible for acetylene hydrogenation to ethylene. Furthermore, the sites involving direct ethane formation from acetylene could be suppressed by NO x treatment.

Rates and product properties of polyethylene produced by copolymerization of 1-hexene and ethylene in the gas phase with (n-BuCp)2ZrCl2 on supports with different pore sizes

Abstract The effects of catalyst support pore size and reaction conditions ( T =40–100 °C; ethylene pressure=1.4 MPa; 1-hexene concentration=0–47 mol/m 3 ) on gas-phase polymerization rates and product properties were studied. Catalysts were prepared by impregnation of mesoporous molecular sieves (pore sizes of 2.5–20 nm) with methylaluminoxane and ( n -BuCp) 2 ZrCl 2 . Temperature rising elution fractionation, differential scanning calorimetry and size exclusion chromatography were used to characterize the products. The results showed that these catalysts contained multiple types of catalytic sites and that the types of sites were a strong function of the support pore size. Ethylene polymerization and 1-hexene incorporation rates were strong functions of support pore size, 1-hexene concentration, and temperature. Large-pored catalysts had higher 1-hexene incorporation rates and the rate of 1-hexene incorporation was a function of polymerization time. Highest polymerization rates were obtained at 80 °C and 1-hexene concentration of 4–12 mol/m 3 ; high 1-hexene concentrations resulted in large decreases in polymerization rates.

Simulation of pervaporation membrane reactors for liquid phase synthesis of ethyl tert-butyl ether from tert-butyl alcohol and ethanol

Abstract The synthesis of ethyl tert -butyl ether (ETBE) from a liquid phase reaction between ethanol (EtOH) ethyl and tert -butyl alcohol (TBA) in pervaporation membrane reactors (PVMRs) is discussed in this paper. Three modes of PVMR operation; semi-batch reactor (SBR), continuous stirred tank reactor (CSTR) and plug flow reactor (PFR) were modeled using kinetic parameters of the synthesis over β-zeolite and permeability data for a polyvinyl alcohol (PVA) membrane from our previous work. Good agreement between experimental and simulation results for the SBR mode was obtained. The study focused on comparing PVMR performances between two modes of continuous flow operation for various operating parameters, i.e. ratio of catalyst weight to total molar feed rate ( φ ), ratio of membrane area to catalyst weight ( δ ), operating temperature and feed composition. It was found that the CSTR mode shows superior performance to the PFR mode only within some ranges of operating conditions. To obtain high ETBE yields, it is best to operate the PVMRs at low temperature with a high ratio of membrane area to catalyst weight ( δ ) and with the feed ratio of EtOH and TBA at the stoichiometric value or slightly higher.

Influence of synthesis conditions on the preparation of zirconia powder by the glycothermal method

Nanocrystalline zirconia powders have been prepared by the reaction of zirconium n-propoxide in 1,4-butanediol and 1,5-pentanediol at 300 °C for 2 h. The influences of concentration of zirconium n-propoxide in the solution and drying condition on primary and secondary particle size, and pore system of the powders were investigated. When 1,4-butanediol was used, increasing the concentration of zirconium n-propoxide increased the primary and secondary particle size and BET surface area while the physical properties of zirconia prepared in 1,5-pentanediol were not affected by such factors. To investigate the effect of drying method, glycol was removed from the autoclave at reaction temperature instead of by the conventional process in which the product is washed in methanol and air-dried. This change improved the pore system of powders prepared in 1,5-pentanediol, probably through the reduction of coagulation among the ultrafine particles during the drying process.

Carbon deposits effects on the selective catalytic reduction of NO over zeolites using temperature programmed oxidation technique

Abstract Temperature programmed oxidation (TPO) technique was adapted to investigate selective catalytic reduction (SCR) of NO over various types of zeolites. SCR reactions in this study were separated into two steps: (1) hydrocarbon deposition to form carbonaceous deposits on catalyst surface and (2) oxidation and/or reduction of the carbon deposits. From this technique, it was found that carbon deposits must be involved in the SCR because both N2 and CO2 were detected during oxidation of the hydrocarbon exposed zeolites with NO+O2. It was also observed that Cu-ZSM-5 and H-MOR induced more coke formation than H-ZSM-5 and HY whereas H-ZSM-5 has a higher NO reduction rate than the others. The amount of carbonaceous deposit depends on hydrocarbon type but the NO reduction seemed to be independent of the coke precursor. When NO+O2 was added during exposure of hydrocarbon to Cu-ZSM-5, the carbonaceous structure was not change but the deposition rate is dramatically increased. It is suggested that NO+O2 accelerates hydrocarbon deposition or that coke may be formed in another route involving SCR. In addition, N2 was detected during TPO by O2 of this exposed zeolite. This indicates that nitrogen compounds have to be either part of carbonaceous deposit or they may adsorb on the deposit in the zeolite. Further study of incorporation of nitrogen in the carbon deposit or on zeolite will be carried out.