Surface Modification of SiO2 for Highly Dispersed Pd/SiO2 Catalyst.

Surface modification of SiO2 supports was shown to significantly affect the properties of Pd/SiO2 catalysts. The surface of SiO2 can be modified by various pretreatment methods. In this study, the effect of different calcination temperatures on support surface was investigated. Pd supported on pretreated SiO2 was characterized by H2 temperature-programmed reduction (TPR), XRD, CO chemisorption measurements, and field-emission transmission electron microscopy (FE-TEM). The silanol group (-OH), which is one of the functional groups of SiO2, interferes with the reduction of palladium because it strongly bonds with palladium ions (-PdO) during the preparation of the catalyst. Due to the complete removal of silanol (Si-OH) groups following calcination at 700 °C, the metal reducibility was enhanced, and the catalyst pretreated at this calcination temperature exhibited the highest metal dispersion of 13.02%. Further, to confirm the catalytic activity of the prepared catalysts, hydrogenation of D-glucose was conducted. The HPLC results demonstrated that Pd/SiO2_700 has the highest catalytic activity toward hydrogenation of D-glucose. Therefore, it was confirmed that the removal of silanol groups increase the metal dispersion and catalytic activity of Pd/SiO2 catalyst.

Influence of Synthetic Parameters on the Particle Size and Distribution of Pd in Pd/Al2O3 Catalysts.

The increasing role of catalysis by noble metals coupled with their high price requires the development of cheaper and more effective catalysts, e.g., highly dispersed supported catalyst. Herein, Pd supported on Al2O3 catalysts prepared by deposition-precipitation under different conditions were subjected to X-ray diffraction, N2-physisorption, NH3/CO2 temperature programmed desorption, CO-chemisorption, and field-emission transmission electron microscopy analyses, which revealed that the size and distribution of Pd particles were influenced by Al2O3 support type (particle size and phase transition) and preparation conditions (metal precursor type, pH value, and solution temperature). The Pd/Al2O3 catalysts were prepared using type A (particle size = 3 micron) or type B (particle size = 20 nm) as a support and PdCl2 (PC) or Pd(NO3)2·2H2O (PN) as a Pd precursor, respectively. In XRD results, type A (particle size = 3 micron) Al2O3 had γ and  phase, and type B (particle size = 20 nm) Al2O3 had only thermally stable γ phase. In addition, Pd dispersion and crystallite size showed an obvious dependence on pH value, solution temperature and attractive/repulsive forces between the functional groups of Al2O3 and Pd precursors. Optimal results were obtained using PdCl2 (PC) as a Pd precursor and type B (particle size = 20 nm) as a support at 60 °C and pH 5.5.

Synthesis of PbMoO4 Nanoparticles Using a Facile Surfactant-Assisted Microwave Process and Their Photocatalytic Activity.

Lead molybdate (PbMoO4) materials were successfully synthesized using a facile surfactant-assisted microwave process and characterized by XRD, Raman, PL, BET and DRS. We also investigated the photocatalytic activity of these materials for the decomposition of Rhodamine B under UV-light irradiation. The XRD and Raman results revealed the successful synthesis of 42­69 nm, well-crystallized PbMoO4 crystals with a facile surfactant-assisted microwave process. The PbMoO4 catalysts prepared using microwave process enhanced the photocatalytic activity compared to PbMoO4 catalyst prepared by hydrothermal method. The PbMoO4 catalyst prepared at 100 °C showed the highest photocatalytic activity. The PL peak was appeared at about 540 nm for all catalysts and the excitonic PL signal was proportional to the photocatalytic activity for the decomposition of Rhodamine B.

Synthesis of Glycerol Carbonate by Transesterification of Glycerol with Urea Over Zn/Al Mixed Oxide.

Reactions of glycerol carbonate using glycerol and urea have been carried out previously using ZnSO4 and ZnO catalysts, and high yields have been reported using ZnSO4 as catalyst. However, this salt is soluble in glycerol, and recycling of catalyst is difficult after the reaction. In this study, we prepared a mixed metal oxide catalyst using Zn and Al, and this catalyst consisted of a mixture of ZnO and ZnAl2O4. We confirmed the conversion of glycerol and the yield of glycerol carbonate of the amount of Al. As a result, we obtained a yield of 82.3% and a conversion of 82.7%. In addition we obtained high yield in recycling of catalyst. The yield of the glycerol carbonate increases with an increase of acid and base site of catalysts and the highest catalytic activity was obtained when acid/base ratio was approx. 1. From this result, we may conclude that the acid and base site density and ratio of catalysts were very important parameters in the synthesis of glycerol carbonate from urea and glycerol.

Liquid Hydrogenation of Maleic Anhydride with Pd/C Catalyst at Low Pressure and Temperature in Batch Reactor.

Succinic acid (SA) produced from hydrogenation of maleic anhydride (MAN) is used widely in manufacturing of pharmaceuticals, agrochemicals, surfactants and detergent, green solvent and biodegradable plastic. In this study, we performed that liquid hydrogenation of MAN to SA with 5 wt% Pd supported on activated carbon (Pd/C) at low pressure and temperature. The synthesis of SA was performed in aqueous solution while varying temperature, pressure, catalytic amount and agitation speed. We confirmed that the composition of the products consisting of SA, maleic acid (MA), fumaric acid (FA) and malic acid (MLA) depends on the process. The catalytic characteristics were analyzed by TGA, TEM.

Hydrogenolysis of Glycerol to Propylene Glycol on Nanosized Cu-Zn-Al Catalysts Prepared Using Microwave Process.

Cu-Zn-Al catalysts were prepared using microwave-assisted process and co-precipitation methods. The prepared catalysts were characterized by XRD, BET, XPS and TPD of ammonia and their catalytic activity for the hydrogenolysis of glycerol to propylene glycol was also examined. The XRD patterns of Cu/Zn/Al mixed catalysts show CuO and ZnO crystalline phase regardless of preparation method. The highest glycerol hydrogenolysis conversion is obtained with the catalyst having a Cu/Zn/Al ratio of 2:2:1. Hydrogen pre-reduction of catalysts significantly enhanced both glycerol conversions and selectivity to propylene glycol. The glycerol conversion increased with an increase of reaction temperature. However, the selectivity to propylene glycol increased with an increase of temperature, and then declined to 30.5% at 523 K.

Synthesis of PbMoO4 nanoparticles by microwave-assisted hydrothermal process and their photocatalytic activity.

Lead molybdate (PbMoO4) was successfully synthesized using a microwave-assisted method and characterized by XRD, Raman spectroscopy, SEM, PL and DRS. We also investigated the photocatalytic activity of these materials for the decomposition of Rhodamin B under UV-light irradiation. The XRD and Raman results revealed the successful synthesis of 42-52 nm, well-crystallized PbMoO4 crystals with the microwave-assisted hydrothermal method. The PbMoO4 catalysts prepared using the microwave-assisted process enhanced the photocatalytic activity compared to that prepared by hydrothermal method and the catalysts prepared at a solution pH = 11 and temperature of 105 degrees C showed the highest photocatalytic activity. The PL peaks appeared at about 540 nm for all catalysts and the excitonic PL signal was proportional to the photocatalytic activity for the decomposition of Rhodamin B.

Photocatalytic decomposition of methyl orange over nanosized perovskite-type oxides under visible light irradiation.

In this study, we have investigated the photocatalytic activity for the decomposition of methyl orange on the LaCoO3 perovskite-type oxides prepared using sol-gel method at different conditions. From the results of UV-Vis DRS, all the catalysts have the similar absorption spectrum up to visible region. The LaCoO3 catalyst prepared at 1.5 mol of malic acid and calcined at 350 degrees C shows the highest activity. The amount of photo absorption in the visible region is correlated with the photocatalytic activity. In addition, the chemisorbed oxygen plays an important role on the photocatalytic decomposition of methyl orange and the higher are the contents of chemisorbed oxygen, the better shows the performance of photocatalyst.

Catalytic combustion of benzene over nanosized LaMnO3 perovskite oxides.

In this study, LaMnO3 perovskite type oxides were successfully prepared using the malic acid method. The oxides were characterized by TG/DTA, XRD, XPS, TEM and H2-TPR and their catalytic activities for the combustion of benzene were determined. Almost all of the catalysts showed perovskite crystalline phase and had a particle size of 15-60 nm. The LaMnO3 catalysts prepared with more than 1.0 mol of malic acid showed the highest activity and the conversion reached almost 100% at 310 degrees C. The catalysts were modified to enhance the activity by substituting the metal at the A or B site of the perovskite oxides. In the LaMnO3-type catalyst, the partial substitution of Sr into site A enhanced the catalytic activity during benzene combustion. In addition, the partial substitution of Co into site B also increased the catalytic activity and the catalytic activity was in the following order: Co > Cu > Fe in the LaMn1_xBxO3(B = Co, Fe, Cu) type catalysts.

Synthesis of Pb-substituted LaCoO3 nanoparticles by microwave process and their photocatalytic activity under visible light irradiation.

In this study, nanosized lead-substituted perovskite type oxides, La1_xPbxCoO3, were successfully synthesized using a microwave-assisted method and characterized by TG/DTA, XRD, XPS, TEM and DRS. We also investigated the photocatalytic activity of these oxides for the decomposition of methyl orange. From XRD results, metal replacement with the Pb ion in the crystal lattice does not change the high crystallinity of the perovskite structure. When Pb ions are substituted into site A, the particle size decreased when compared to lead-free LaCoO3 perovskite type oxide. In the of UV-Vis DRS analysis, all the catalysts displayed the similar absorption spectrum up to the visible region and the absorption band shifted to a higher wavelength on the lead-substituted LaCoO3 perovskite oxides when compared to the lead-free LaCoO3 oxide. From XPS results, chemisorbed oxygen was shown to play an important role in the photocatalytic decomposition of methyl orange and the higher chemisorbed oxygen content, the better the performance of the photocatalyst.

Catalytic combustion of benzene over copper oxide supported on SBA-15 using chelating method.

The catalytic combustion of benzene over copper oxide supported on SBA-15 was investigated. The catalysts were prepared by the using chelating method and characterized. It is clear that the loading of CuO on the silica matrix drastically decreases the surface area and pore volume of the catalysts, as would be expected for the incorporation of CuO. The catalytic activity increased with an increase of CuO loading ratio. When CuO loading reached 5.8 wt%, the total conversion temperature was lowered to 350 degrees C.

Synthesis of TiO2 supported on SBA-15 using different method and their photocatalytic activity.

SBA-15 mesoporous materials were successfully prepared by the conventional hydrothermal method and TiO2 nanoparticles were supported on them using different loading methods. The synthesized materials were characterized and their activity as photocatalysts for the decomposition of methylene blue was evaluated. The loading of titanium dioxide on the framework of SBA-15 makes the pore diameter and pore volume decrease compared to that of SBA-15. The chelating method causes the support to have a much better dispersion capacity for TiO2 particles as compared to the other two methods. The TiO2 supported by chelating method showed the highest photocatalytic activity among the photocatalysts prepared by different method.

Effect of surface properties of TiO2 on the performance of Pt/TiO2 catalysts for furfural hydrogenation.

Hydrogenation of biomass-derived furfural is an important process in biofuel production. Herein, different Pt-supported TiO2 morphologies: nanorod (NR), nanoparticle (NP), and hollow microsphere (HMS) were prepared by the impregnation-chemical reduction method. The furfural conversion increased with an increase of Pt dispersion. However, cyclopentanone selectivity was affected by TiO2 properties, the strong metal-support interaction (SMSI) effect, and the reaction conditions. The Pt/TiO2 NR catalyst exhibited the highest cyclopentanone selectivity of 50.4%. Based on the H2-temperature programmed desorption (H2-TPD) and X-ray photoelectron spectroscopy (XPS) results, the Pt/TiO2 NR catalyst showed a SMSI effect, which was introduced by the chemical reduction method. We suggest that electron charge transfer from Ti species to Pt in the Pt/TiO2 NR catalyst affects the cyclopentanone selectivity by controlling the adsorption strength between the reactant and the Pt surface, thus retarding the formation of byproducts.

Effects of chlorinated Pd precursors and preparation methods on properties and activity of Pd/TiO2 catalysts.

We investigated the effects of Pd precursors and preparation methods on the physicochemical properties and performance of Pd/TiO2 catalysts in the photocatalytic degradation of methyl violet. To confirm the influence of the precursors, Pd/TiO2 catalysts were prepared via chemical reduction (CR) using four different Pd precursors. Additionally, to determine the effects of preparation methods, Pd/TiO2 catalysts were fabricated using K2PdCl4 precursor via three different methods: CR, deposition-precipitation (DP), and impregnation. The CO chemisorption results showed that the catalyst prepared via DP using the K2PdCl4 precursor, i.e., Pd/TiO2_K_DP, displayed the highest Pd dispersion of 12.42% owing to the stable formation of Pd(OH)2, which strongly interacted with the -OH groups on the TiO2 support. Although the catalyst prepared via CR using the Pd(NH3)4Cl2·H2O (PA) precursor, i.e., Pd/TiO2_PA_CR, had the lowest Pd dispersion of 0.7%, it exhibited the highest absorption of 26% after 30 min in the dark. It was found that high Pd2+/Pd0 ratio in dark conditions adversely affected the absorption of MV owing to electrostatic repulsion between the cationic dyes and metal nanoparticles. However, the Pd dispersion and the specific surface area played a key role in the photocatalytic activity under UV irradiation. Pd/TiO2_K_CR with higher Pd dispersion showed the highest photocatalytic activity and reaction rate of 0.0212 min-1.

Kinetic Study of CO2 Hydration by Small-Molecule Catalysts with A Second Coordination Sphere that Mimic the Effect of the Thr-199 Residue of Carbonic Anhydrase.

Zinc complexes were synthesized as catalysts that mimic the ability of carbonic anhydrase (CA) for the CO2 hydration reaction (H2O + CO2 → H+ + HCO3-). For these complexes, a tris(2-pyridylmethyl)amine (TPA) ligand mimicking only the active site, and a 6-((bis(pyridin-2-ylmethyl)amino)methyl)pyridin-2-ol (TPA-OH) ligand mimicking the hydrogen-bonding network of the secondary coordination sphere of CA were used. Potentiometric pH titration was used to determine the deprotonation ability of the Zn complexes, and their pKa values were found to be 8.0 and 6.8, respectively. Stopped-flow spectrophotometry was used to confirm the CO2 hydration rate. The rate constants were measured to be 648.4 and 730.6 M-1s-1, respectively. The low pKa value was attributed to the hydrogen-bonding network of the secondary coordination sphere of the catalyst that mimics the behavior of CA, and this was found to increase the CO2 hydration rate of the catalyst.

Growth mechanism of SnC2H4O2 nanowires prepared by the polyol process as SnO2 precursor nanowires.

Tin oxide (SnO2) nanowires are produced by the calcination of tin glycolate (SnC2H4O2) nanowires, which are synthesized with tin oxalate (SnC2O4) and ethylene glycol via the so-called polyol process. In this study, the growth mechanism of SnC2H4O2 nanowires was investigated by monitoring the synthesis using scanning and transmission electron microscopy. The length and diameter of the nanowires were 9.25 µm and 0.37 µm, respectively; the former increased at a rate of 1.85 µm h-1 but the latter did not increase over time. Fourier-transform IR spectroscopy showed that the nanowires were composed of SnC2H4O2 instead of SnC2O4. Changes in the components of the reaction solution were also confirmed by 1H NMR, 13C NMR, and high-performance liquid chromatography. SnC2H4O2 was formed by the substitution of the oxalate coordinated to tin by ethylene glycolate, which was produced by the deprotonation of ethylene glycol. In this reaction, oxalate gradually changed to formic acid and carbon dioxide, and SnC2H4O2 grew as a nanowire through O-Sn-O bond formation. In addition, when ethylene glycol was mixed with 1,2-propanediol, branched SnC2H4O2 nanowires were formed. The branching was due to the interference of the methyl group of 1,2-propanediol with the growth of bundle-type nanowires. The branched nanowires had a higher surface area-to-mass ratio than the bundled ones based on dispersion measurements. Knowledge of the growth mechanism and reaction conditions that affect morphology would be valuable in modifying the physical and electrical properties of metal oxide nanowires.

Kinetic study of catalytic CO2 hydration by metal-substituted biomimetic carbonic anhydrase model complexes.

The rapid rise of the CO2 level in the atmosphere has spurred the development of CO2 capture methods such as the use of biomimetic complexes that mimic carbonic anhydrase. In this study, model complexes with tris(2-pyridylmethyl)amine (TPA) were synthesized using various transition metals (Zn2+, Cu2+ and Ni2+) to control the intrinsic proton-donating ability. The pKa of the water coordinated to the metal, which indicates its proton-donating ability, was determined by potentiometric pH titration and found to increase in the order [(TPA)Cu(OH2)]2+ < [(TPA)Ni(OH2)]2+ < [(TPA)Zn(OH2)]2+. The effect of pKa on the CO2 hydration rate was investigated by stopped-flow spectrophotometry. Because the water ligand in [(TPA)Zn(OH2)]2+ had the highest pKa, it would be more difficult to deprotonate it than those coordinated to Cu2+ and Ni2+. It was, therefore, expected that the complex would have the slowest rate for the reaction of the deprotonated water with CO2 to form bicarbonate. However, it was confirmed that [(TPA)Zn(OH2)]2+ had the fastest CO2 hydration rate because the substitution of bicarbonate with water (bicarbonate release) occurred easily.

Improvements of Pd/C Catalyst Support Characteristics by Various Physical Dispersion Methods.

Pd/C catalysts were prepared by ion exchange in aqueous solution. Physical dispersion methods including sonication, high share mixer and stirrer were used for though high dispersion of carbon. The physical properties of the prepared Pd/C particles were investigated by BET, XRD, and FE-TEM. The dispersion of Pd nanoparticles on carbon was measured on the basis of CO adsorption capacity using a pulse technique. FE-TEM micrographs showed that Pd nano particles possessed a spherical morphology with a narrow size distribution, with particles sizes ranging from 2-25 nm. The Pd particles prepared using sonication and high share mixer are well dispersed compared to the stirrer method. In addition, metal dispersions as calculated by CO uptake were 11.3, 20.4, and 25.0% for the stirrer, sonication and high share mixer methods, respectively.

Catalytic Oxidation of Benzene Over LaCoO3 Perovskite-Type Oxides Prepared Using Microwave Process.

LaCoO3 perovskite type oxides were successfully prepared using microwave-assisted method, characterized by TG/DTA, XRD, XPS and H2-TPR and their catalytic activities for combustion of benzene were determined. Almost of catalyst showed perovskite crystalline phase and 13-84 nm particle size. LaCoO3 catalysts prepared by microwave-assisted method showed the highest activity and the conversion reached almost 100% at 360 degrees C. In the LaCoO3-type catalyst, the partial substitution of Sr into site A enhanced the catalytic activity on the combustion of benzene. The higher amount of the chemisorbed oxygen was, the better the performance of the combustion catalyst. The catalytic activity of perovskite-type oxides showed a good relationship with the results of H2-TPR and XPS measurement.

Carbon Nano Tube Supported Pd Catalyst: Effect of Support Textual Properties with Pre-Treatment Method of Pd Particle.

The aim of this work is to be compared the effect of supports textural properties with pre-treatment method on dispersion of Pd particle. The CNTs were functionalized by different concentration of acid in order to obtain materials with different chemical and physical properties. The characteristics of functionalized CNTs were investigated by FT-IR and Rama spectropy. The Pd/CNTs catalysts prepared on support having the different surface properties were characterized by XRD, FE-TEM and CO-chemisorption. When pretreated 8M concentration, the CNTs has the highest amount of oxygen functional group and ID/IG ratio, in this study. Pd/CNT8M has high dispersion and small particle size. From these results, we confirmed that characteristics of Pd/CNTs catalyst such as particle size and dispersion of Pd are influenced by density of oxygen functional group and disorder of CNTs. And we have observed that acid treatment concentration of 8M is sufficient to functionalize the CNTs by introducing -COOH group of CNTs surfaces.