Low-temperature synthesis of rhodium phosphide on alumina and investigation of its catalytic activity toward the hydrodesulfurization of thiophene

In this study, the low-temperature synthesis of rhodium phosphide (Rh2P) on alumina (Al2O3) using triphenylphosphine (TPP) as a phosphorus (P) source and its catalytic activity toward hydrodesulfurization (HDS) were investigated to prepare a highly active HDS catalyst. TPP was more easily reduced than phosphate, and Rh2P was formed in the P(T)/Rh/Al2O3 catalyst prepared from TTP at lower temperature as compared with the temperature required by Rh-P(A)/Al2O3 catalyst prepared from a phosphate precursor. However, after reduction at a low temperature (450 °C), excess P covered the surface of Rh2P. The optimal reduction temperature for HDS rate of the P(T)/Rh/Al2O3 catalyst (650 °C) was lower than that of the Rh-P(A)/Al2O3 catalyst (800 °C). Furthermore, this temperature was slightly higher than the optimal reduction temperature for CO uptake (600 °C). These results are explained as follows: HDS rate is increased by both elimination of excess P on the active sites at higher reduction temperatures and enhancement of the crystallinity of Rh2P. Furthermore, because the particle size of the P(T)/Rh/Al2O3 catalyst (ca. 1.2 nm) was substantially smaller than that of the Rh-P(A)/Al2O3 catalyst, the P(T)/Rh/Al2O3 catalyst exhibited greater HDS rate compared with the Rh-P(A)/Al2O3 catalyst

Pure hydroxyapatite synthesis originating from amorphous calcium carbonate

We report a synthesis strategy for pure hydroxyapatite (HAp) using an amorphous calcium carbonate (ACC) colloid as the starting source. Room-temperature phosphorylation and subsequent calcination produce pure HAp via intermediate amorphous calcium phosphate (ACP). The pre-calcined sample undergoes a competitive transformation from ACC to ACP and crystalline calcium carbonate. The water content, ACC concentration, Ca/P molar ratio, and pH during the phosphorylation reaction play crucial roles in the final phase of the crystalline phosphate compound. Pure HAp is formed after ACP is transformed from ACC at a low concentration (1 wt%) of ACC colloid (1.71 < Ca/P < 1.88), whereas Ca/P = 1.51 leads to pure beta-tricalcium phosphate. The ACP phases are precursors for calcium phosphate compounds and may determine the final crystalline phase

Development of Highly Active New Hydrodesulfurization Catalysts for Prevention of Acid Rain : Supported Noble Metal Catalysts

The catalytic activities and performance of noble metals supported on various carriers such as metal oxides, carbons, zeolite, Al-pillared clays and mesoporous silica for the hydrodesulfurization (HDS) of thiophene as a model HDS reaction for petroleum were investigated in order to develop highly active new HDS catalysts. It was revealed that sulfided Rh supported on SiOB2B, amorphous carbon (Am.C), Pt supported on HZSM-5, MCM-41 and Rh supported on Al-PILM (montmorillonite) showed high and stable activities for the HDS of thiophene. The activities of these catalysts were higher than that of commercial CoMo/AlB2BOB3B HDS catalyst. Therefore, some kind of supported noble metal catalysts have high potential for new HDS catalysts for petroleum.特集 : 「2003年度実施の地域との共同研究の報告

白金担持金属酸化物触媒によるチオフェンの水素化脱硫反応

The catalytic activities of platinum (Pt) supported on various metal oxides (MOX; Al2O3, SiO2, TiO2, MgO and ZnO) for hydrodesulfurization (HDS) of thiophene were investigated. HDS activities of supported Pt catalysts were examined at 350oC by using conventional fixed bed flow reactor under atmospheric pressure. The order of HDS activities of Pt/MOX was as follows; Pt/Al2O3 > Pt/SiO2 > Pt/TiO2 > Pt/MgO > Pt/ZnO. Catalytic properties of MOX supports and Pt/MOX were evaluated by nitrogen adsorption, decomposition of 2-propanol (2-PA), XRD and hydrogen adsorption. It was revealed that HDS activities of Pt/MOX catalysts were not correlated to BET surface area and acid-base properties of MOX but these were strongly correlated to the dispersion of Pt on MOX.種々の金属酸化物(MOX;Al2O3,SiO2,TiO2,MgO,ZnO)に担持した白金(Pt)触媒のチオフェン水素化脱硫(HDS)反応に対する活性(350oC)について検討した.担持白金触媒のHDS活性は常圧固定床流通式反応装置を用いて検討した.その結果,Pt/MOXのHDS活性の序列はPt/Al2O3 > Pt/SiO2 > Pt/TiO2 > Pt/MgO > Pt/ZnOとなることがわかった.MOX担体の表面積,酸塩基特性およびPtの分散度を窒素吸着法,2-プロパノールの分解反応,XRDおよび水素吸着法で評価したところ,Pt担持MOX触媒のHDS活性はMOXのBET表面積および酸塩基特性には依存しないが,Ptの分散度に強く依存することが明らかとなった.投稿論

Formation of active sites and hydrodesulfurization activity of rhodium phosphide catalyst: Effect of reduction temperature and phosphorus loading

Effects of reduction temperature and phosphorus loading on rhodium phosphide (Rh2P) formation and on the catalytic activity of Rh-xP catalysts for hydrodesulfurization (HDS) were investigated to prepare highly active HDS catalysts. Analysis of the Rh-xP catalysts showed that a suitable P loading for HDS activity is 1.5 wt%—four times greater than that of an Rh catalyst. Temperature-programmed reduction and X-ray diffraction analyses of the Rh-xP catalysts showed that Rh2P is readily formed in catalysts with higher P loading. In contrast, the results of transmission electron microscopy observation and CO adsorption experiments indicated that the Rh2P particle size increased with increasing P content. Thus, the high HDS activity of the Rh-1.5P catalyst was explained by the formation of small Rh2P at a relatively low reduction temperature (550 °C

Key particle properties of shells for cadmium chemisorption

Previous studies on cadmium adsorption of calcium carbonate have found that polymorph, and, crystallinity are influential factors for adsorbing cadmium ions. The predominant factor for cadmium adsorption has yet to be elucidated because these factors are linked. To overcome this, here each factor is investigated separately. First, atmospheric grinding prepared surf clam (aragonite phase) and scallop (calcite phase) shells with similar crystallite sizes and specific surface areas. Using adsorption isotherm models, kinetics, X-ray diffraction analysis, and TEM observations, both calcite and aragonite react with cadmium to form cadmium carbonate. The chemisorption follows the adsorption mechanism reported in the literature. Based on the Langmuir isotherm model fitting, the maximum adsorbed amount for the ground surf clam shells is 633.3 mg/g, while that for scallop shells is 195.8 mg/g. Then fine surf clam shell particles with a similar specific surface area, and with a relatively wide range of the aragonite ratio, and crystallite size are prepared via a combination of grinding and a subsequent calcination process. Our experiments where one explanatory variable is changed at a time demonstrate that the polymorph ratio and crystallite size of the ground shells play key roles in the chemisorption

Effect of aluminum modification on catalytic performance of Pt supported on MCM-41 for thiophene hydrodesulfurization

The catalytic activities and properties of platinum supported on siliceous MCM-41 and Al-modified MCM-41, such as Al-incorporated MCM-41 (AlMCM-41) and alumina-modified MCM-41 (Al_2O_3-MCM-41), for the hydrodesulfurization (HDS) of thiophene were investigated. Al_2O_3-MCM-41 was prepared by an impregnation method using aluminum nitrate (Al(NO_3)_3·9H_2O) aqueous solution. Pt/Al_2O_3-MCM-41 catalyst showed high and stable activity for HDS of thiophene and this activity was remarkably higher than that of a commercial CoMo/Al_2O_3 HDS catalyst. The catalysts were characterized by XRD, hydrogen adsorption, ammonia-TPD, 2-propanol dehydration, cumene cracking and FT-IR. Dispersion of platinum on Al_2O_3-MCM-41 was remarkably higher than on MCM-41 or on AlMCM-41. It was revealed that the acidity of Al_2O_3-MCM-41 was higher than that of MCM-41 or of AlMCM-41. Furthermore, it was observed that there exist Brønsted acid sites on Al-modified MCM-41. FT-IR spectra of thiophene adsorbed on Al-modified MCM-41 support indicates that thiophene molecules interact with Brønsted acid sites on Al-modified MCM-41. It was found that the HDS activity of Pt/quartz mixed mechanically with Al-modified MCM-41 catalyst was higher than that calculated. This suggests that there exists spillover hydrogen on supportedPt catalysts in the HDS of thiophene. Results revealed that the high activity of Pt/Al_2O_3-MCM-41 catalyst for HDS reaction is due to good harmony of high dispersion of Pt particles and Brønsted acidity of the support

Catalytic properties of metallosilicates

Metallosilicates with MFI structure containing metal atoms such as Ni, Co, Cu, Zn-Cu and Zn in framework have been synthesized with various metal/silicone (Me/Si) ratios (up to 0.1). The acidities of H-form metallosilicates were evaluated by some acid-catalyzed reactions (decomposition of 2-propanol, cracking of cumene and isomerization of 1-butene). The Zn-Si catalyst showed the highest acidities among various metallosilicates. In the metallosilicates-supported noble metal catalysts, 5%Pt/Zn-Si and 0.1%Pd/Cu-Si catalysts showed the highest activities for hydrodesulfurization of thiophene and hydrodechlorination of chlorobenzene, respectively.研究報

Preparation of highly active alumina-pillared clay montmorillonite- supported platinum catalyst for hydrodesulfurization

Effect of Pt precursor and pretreatment on hydrodesulfurization (HDS) activity of Pt/Al-PILM catalyst was examined to prepare highly active Pt-supported HDS catalyst. The order of HDS activities of Pt/alumina-pillared clay montmorillonite (Al-PILM) catalysts prepared by various Pt precursors was Pt(C_5H_7O_2)_2 > H_2PtC_｛l6｝ · 6H_2O > [Pt(NH_3)_4](NO_3)_2 > [Pt(NH_3)_4]C_｛l2｝ · H_2O > H_2Pt(OH)_6. This order was in accordance with that of Pt dispersion. Thus, high Pt dispersion is essential factor to prepare highly active Pt/Al-PILM catalyst for HDS reaction. On the other hand, the effect of pretreatment on the HDS activities of Pt/Al-PILM catalysts prepared by various Pt precursors was also evaluated. The UC-TPS Pt/Al-PILM catalyst showed the highest HDS activity among various pretreated Pt/Al-PILM catalysts, in which uncalcined catalyst was sulfided by temperature programmed sulfidation (TPS). We assumed that high HDS activity of UC-TPS Pt/Al-PILM catalyst is caused by partly sulfided Pt particle with high dispersion. It is concluded that the highly active Pt/Al-PILM catalyst for the HDS reaction could be prepared by using Pt(C_5H_7O_2)_2 as a precursor and UC-TPS treatment

Preparation of highly active AlSBA-15-supported platinum catalyst for thiophene hydrodesulfurization

The catalytic activities of various noble metals (Pt, Pd, Rh, and Ru) supported on siliceous SBA-15 and Al-containing SBA-15 (AlSBA-15) for hydrodesulfurization (HDS) of thiophene at 350 C were investigated. AlSBA-15 was prepared by a grafting method using aluminum isopropoxide (Al(OC3H7)3) hexane solution. The HDS activity of Pt/AlSBA-15 catalyst was the highest among those of various supported noble metal catalysts, and this activity was higher than that of commercial CoMo/Al2O3 HDS catalyst. The catalysts were characterized by XRD analysis, hydrogen adsorption, 2-propanol dehydration, cumene cracking, and FT-IR. Dispersion of Pt on SBA-15 was remarkably enhanced by Al grafting. It was revealed that the acidity of AlSBA-15 was higher than that of SBA-15. Furthermore, Brønsted acid sites were observed on AlSBA-15. FT-IR spectra of thiophene adsorbed on AlSBA-15 indicate that thiophene molecules interact with Brønsted acid sites on the surface of AlSBA-15 and that the strength of this interaction was stronger than that of SBA-15. Based on these results, thiophene molecules activated on Brønsted acid site of AlSBA-15 and hydrogen molecules activate to form spillover hydrogen on Pt particles in Pt/AlSBA-15 catalyst in the HDS of thiophene