Joongjai Panpranot

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.

Improvement of early cell adhesion on Thai silk fibroin surface by low energy plasma.

Low energy plasma has been introduced to treat the surface of Thai silk fibroin which should be enhanced for cell adhesion due to its native hydrophobic surface. Plasma surface treatment could introduce desirable hydrophilic functionalities on the surface without using any chemicals. In this work, nitrogen glow discharge plasma was generated by a low energy AC50Hz power supply system. The plasma operating conditions were optimized to reach the highest nitrogen active species by using optical emission spectroscopy. X-ray photoelectron spectroscopy (XPS) revealed that amine, hydroxyl, ether, and carboxyl groups were induced on Thai silk fibroin surface after plasma treatment. The results on Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy confirmed that the plasma treated effects were only on the outermost layer since there was no change in the bulk chemistry. The surface topography was insignificantly changed from the detection with atomic force microscopy (AFM). The plasma-treated effects were the improved surface wettability and cell adhesion. After a 90-s treatment, the water contact angle was at 20°, while the untreated surface was at 70°. The early cell adhesion of L929 mouse fibroblast was accelerated. L929 cells only took 3h to reach 100% cell adhesion on 90 s N2 plasma-treated surface, while there was less than 50% cell adhesion on the untreated Thai silk fibroin surface after 6h of culture. The cell adhesion results were in agreement with the cytoskeleton development. L929 F-actin was more evident on 90 s N2 plasma-treated surface than others. It could be concluded that a lower energy AC50Hz plasma system enhanced early L929 mouse fibroblast adhesion on Thai silk fibroin surface without any significant change in surface topography and bulk chemistry.

NaOH modified WO3/SiO2 catalysts for propylene production from 2-butene and ethylene metathesis

A WO3/SiO2 catalyst is used in industry to produce propylene from 2-butene and ethylene metathesis. Catalysts with various WO3 loading (4% to 10%) were prepared by impregnation and tested for the metathesis of ethene and trans-2-butene. Ion exchange of NaOH onto the WO3/SiO2 catalyst was used to mitigate the acidity of the catalysts in a controlled way. At low WO3 loading, the treatment with large amounts of NaOH resulted in a significant decrease in metathesis activity concomitant with significant W leaching and marked structural changes (XRD, Raman). At higher WO3 loading (6% to 10%), the treatment with NaOH mainly resulted in a decrease in acidity. FT-IR experiments after adsorption of pyridine showed that the Lewis acidic sites were poisoned by sodium. Nevertheless, the metathesis activity remained constant after the NaOH treatment. This suggested that the remaining acidity on the catalyst was enough to ensure the efficient formation of the carbene active sites. Interestingly, Na poisoning resulted in some modification of the selectivity. The mitigation of acidity was shown to favor propene selectivity over the formation of isomerization products (cis-2-butene, 1-butene, etc.). Moreover, treatment with NaOH led to a shorter induction period and reduced coke formation on the WO3/SiO2 catalyst.

Formation of CoAl 2 O 4 nanoparticles via low-temperature solid-state reaction of fine gibbsite and cobalt precursor

Nanocrystalline cobalt aluminate (CoAl2O4) was synthesized by the solid-state reaction method with cobalt chloride hexahydrate (CoCl2 ċ 6H2O) as the source of Co and gibbsite (Al(OH)3) as the source of Al, respectively. The effects of particle size of the starting fine gibbsite (0.6 and 13 µm) and calcination temperatures (450, 550, and 650°C) on the properties of CoAl2O4 were investigated by means of X-ray diffraction (XRD), thermogravimetry analysis and differential thermal analysis (TG/DTA), X-ray photoelectron spectroscopy (XPS), UV-visible absorption spectroscopy (UV-Vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Increasing of calcination temperature promoted the insertion amounts of Co2+ in alumina matrix in CoAl2O4 structure, which resulted in the brighter blue particles and increasing of UV spectra band. The lowest temperature for the formation of nanocrystalline CoAl2O4 particles was 550°C for the solid-state reaction of cobalt chloride and 0.6 µm fine gibbsite.

Production of propylene from an unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts

Abstract An unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts has been studied as an alternative route for the production of propylene. Complete conversion of 2-pentene and propylene yield as high as 88 wt% were obtained under mild reaction conditions at 35°C and atmospheric pressure. Unlike the conventional metathesis of ethylene and 2-butenes in which isomerization is a competing side reaction, the isomerization of 1-butene product from the unconventional metathesis of ethylene and 2-pentene to 2-butenes can further react with excess ethylene in the feed, resulting in additional increase in propylene yield. The secondary metathesis reaction was found to be favored under ethylene/2-pentene (E/2P) molar ratio ≥3 and gas hourly space velocity (GHSV) ≤1000 h−1 at the reaction temperature of 35°C. No catalyst deactivation was observed during the 455 min time-on-stream under the selected reaction conditions.

Role of support nature (γ-Al2O3 and SiO2-Al2O3) on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

Abstract The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re 2 O 7 /γ-Al 2 O 3 and Re 2 O 7 /SiO 2 -Al 2 O 3 catalysts. Both NH 3 temperature-programmed desorption (NH 3 -TPD) and H 2 temperature-programmed reduction (H 2 -TPR) results showed that Re 2 O 7 /SiO 2 -Al 2 O 3 exhibited stronger acidity and weaker metal-support interaction than Re 2 O 7 /γ-Al 2 O 3 . At 35–60 °C, isomerization free metathesis was observed only over Re 2 O 7 /γ-Al 2 O 3 , suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re 2 O 7 /SiO 2 -Al 2 O 3 , hydrido-rhenium species ([Re]-H) were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.

Preparation of improved Ag–Pd/TiO2 catalysts using the combined strong electrostatic adsorption and electroless deposition methods for the selective hydrogenation of acetylene

TiO2-supported Ag–Pd catalysts were prepared by strong electrostatic adsorption (SEA) of Pd followed by electroless deposition (ED) of Ag with incremental surface coverages of Ag (θAg) ranging from 0–0.92. Theoretical monolayer (ML) coverage values (θTheo), assuming monodisperse deposition of Ag on Pd, were equal to experimental coverage values (θExpt) up to approximately θAg = 0.7. Above this value, autocatalytic deposition of Ag on Ag occurred as well as further catalytic deposition of Ag on Pd. The atomic Pd/Ag compositions determined from transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) were in very good agreement with the values from atomic absorption spectroscopy (AAS), decreasing from 16.2 to 1.5 as θAg coverages increased from 0.36 to 0.92 ML. The selectivity of acetylene hydrogenation to ethylene and the turnover frequency for acetylene hydrogenation were maximized at the highest θAg in this study. The uniform deposition of Ag on the surfaces of small Pd particles using the combined methods of SEA and ED resulted in significant improvement of the bimetallic Ag–Pd surface for the selective hydrogenation of acetylene.

Effect of Nano-sized TiO2 Additional Support in WO3/SiO2 Catalyst Systems on Metathesis of Ethylene and Trans-2-Butene to Propylene

TiO2 was employed as an additional support by physical mixing with the WO3/SiO2 catalysts and used in the metathesis of ethylene and trans-2-butene for propylene production. Having nano-sized TiO2 as the additional support could enhance trans-2-butene conversion and propylene yield. The results suggested that tungsten could migrate from an original support and form more well-dispersed surface tetrahedral tungsten oxide species on the additional support, leading to a better dispersion. It was also shown that TiO2 having nano size could provide better spreading of the tungsten species than the micro size. A smaller crystallite size evidenced from XRD and a higher ratio between surface tetrahedral tungsten oxide species over crystalline WO3 evidenced from FT-Raman spectra of the nano-sized TiO2 systems were, among other things, advantageous to metathesis activity improvement of the catalyst. This study offers a guidance of supplementing the existing catalysts as one simple way of improvement in the catalytic performances which can easily be applied in the real metathesis reaction process.Graphical Abstract

Comparison of the behavior of fibroblast and bone marrow-derived mesenchymal stem cell on nitrogen plasma-treated gelatin films.

The attachment and growth behavior of mouse fibroblast (L929) and rat bone marrow-derived mesenchymal stem cell (MSC) on nitrogen plasma-treated and untreated gelatin films was investigated and compared. The gelatin films were prepared by solution casting (0.05% w/v) and crosslinked using dehydrothermal treatment. The crosslinked gelatin films were treated with nitrogen alternating current (AC) 50 Hz plasma systems at various treatment time. The results on the attachment and growth of two cells; L929 and MSC, on plasma-treated gelatin film showed that the number of attached and proliferated cells on plasma-treated gelatin films was significantly increased compared to untreated samples. However, no significant difference between the number of attached L929 and MSC on plasma-treated gelatin was observed. The shorter population doubling time and higher growth rate of cells cultured on plasma-treated film indicated the greater growth of cells, compared to ones on untreated films. The greatest enhancement of cell attachment and growth were noticed when the film was treated with nitrogen plasma for 9 to 15s. This suggested that the greater attachment and growth of both cells on gelatin films resulted from the change of surface properties, i.e. hydrophilicity, surface energy, and chemistry. The suitable water contact angle and oxygen/nitrogen ratio (O/N) of gelatin film for best L929 and MSC attachment were observed at 27-32° and 1.4, respectively. These conditions also provided the best proliferation of cells on plasma-treated gelatin films.

Effect of Dispersion of the Active Phase on the Activity and Coke Formation over WO3/SiO2 Catalysts in the Metathesis of Ethylene and 2-Butene

WO3/SiO2 catalysts with various tungsten loadings were prepared by the incipient wetness impregnation method and studied in the metathesis of ethylene and trans-2-butene as feed to produce propylene. Two different calcination methods were used to modify the dispersion of the tungsten active phase. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen physisorption, ion-exchange titration, FT-Raman, ammonia temperature programmed desorption and temperature programmed oxidation. Better dispersion is obtained from low heating rate calcination. The dispersion of tungsten showed a direct effect on coke formation and was the key factor to improve the stability of the catalysts.Graphical Abstract