Al2O3-supported precious metal catalysts were tested for the oxidative decomposition of NH4+ in water with O3 and the effects of support on the catalytic activity of Pd were investigated. Pd/CeO2 was found to be the best catalyst in terms of activity, selectivity and stability and was more active and selective than Co3O4, which is one of the best catalysts reported so far. The reaction proceeded only in the presence of Cl-. The moderate value of the d-band center relative to the Fermi level of Pd was found to be favorable for the activation of reactants, leading to a high catalytic performance.
“SrFe1-xSnxO3-δ nanoparticles with enhanced redox properties for catalytic combustion of benzene"
Kazutaka Hashimoto, Ryoichi Otomo and Yuichi Kamiya
A series of Sn-substituted strontium ferrate SrFe1-xSnxO3-δ (x = 0, 0.25, 0.50, 0.75 and 1.0) were prepared by the polymerized complex method. Influence of the substitution of Fe in SrFeO3-δ with Sn on structural, redox, and catalytic properties was investigated. X-ray diffraction and 57Fe Mossbauer analyses revealed that the partial substation of Fe with Sn expanded the lattice of the perovskite-type structure, leading to elongation of Fe-O bonds. The partial substitution resulted in the decline of the particle size and the increase of specific surface area. H2-TPR and TG measurements in H2 or O2 flow indicated that the partial substitution significantly accelerated the redox rates of Fe at 500 °C. Due to the increased surface area and enhanced redox properties, the partially substituted SrFe1-xSnxO3-δ showed higher catalytic activity than SrFeO3-δ for combustion of benzene.
“Chitosan-functionalized natural magnetic particle@silica modified with (3-chloropropyl) trimethoxysilane as a highly stable magnetic adsorbent for gold(III) ion"
It is keenly desired to develop an environmentally benign and highly stable magnetic adsorbent for efficient recovery of Au(III) ion from the solution. In the present study, we investigated the synthesis of magnetic adsorbents that the magnetic particles, which was prepared from natural iron sand, were modified with silica layer on which chitosan was fixed through 3-chloropropyltrymethoxysilane (CPTMS) by a sol-gel process. Since the magnetic particles were almost completely covered with the silica layer and chitosan was tightly fixed on it through CPTMS, the adsorbent was highly stable in an acidic solution with pH 3 or lower. Excess CPTMS significantly lowered the adsorption capacity for Au(III) ion and lead to little improvement in the stability. Thus, 1 mmol of CPTMS against 4 mmol of chitosan gave the best magnetic adsorbent in terms of stability and adsorption capacity, of which the maximum was 112 mg g?1 for Au(III) ion at pH 5. The adsorbent showed high selectivity to Au(III) in the solution containing Cu(II) and Zn(II), and it was reusable at least two times with the reduction in the percentage of Au(III) recovery in each reuse was less than 17%. The magnetic adsorbent was separable from the solution simply with an external magnet, while the modification caused a slight decrease of the saturated magnetization.
“Oxidation of Ammonia Nitrogen with Ozone in Water: A Mini Review"
Philip Anggo Krisbiantoro, Koki Kato, Lina Mahardiani, Yuichi Kamiya
Since ammonia nitrogen is a pollutant causing eutrophication, it must be removed from wastewater to develop a sustainable environment and society. Ozonation, which is an oxidation reaction with ozone, is an effective and efficient method for the removal of ammonia nitrogen in wastewater because the reaction can proceed at low temperature and atmospheric pressure. Although the researches in ozonation of ammonia nitrogen have been going on for the last five decades, the reaction mechanism has not yet been well understood, and the papers focusing on the reaction mechanism are very few. In this short review paper, the progress in the oxidation of ammonia nitrogen with ozone both in non-catalytic and catalytic reactions is summarized to provide a better understanding of the reaction mechanism for ozonation of ammonia nitrogen in the water.
“Phosphate recovery from an aqueous solution through adsorption-desorption cycle over thermally treated activated carbon"
In the present study, we tested nine commercially available activated carbons for their abilities to recover phosphate ion from an aqueous solution by a temperature swing method, in which phosphate ion was adsorbed at 303 K, followed by desorption and recovery in pure water at 373 K. While the activated carbon made from coconut shell and manufactured by Nakarai Tesque Inc. (trade name: Charcoal Activated) had a moderate adsorption capacity at 303 K, little amount of phosphate ion was adsorbed on it at 373 K, meaning that it was an appropriate adsorbent for the temperature swing method. Since the adsorbed amounts of phosphate ion for various activated carbons at 303 K were correlated with the number of basic sites on them and were significantly increased as pH of the solution decreased, it is presumed that phosphate ion was adsorbed on the basic sites of the activated carbons with electrostatic interaction mediated by protons. High-temperature thermal treatment of the activated carbon in a vacuum increased the recovered amount of phosphate ion. This increase was brought about by elimination of oxygen-containing functional groups from the activated carbon. By using activated carbon obtained by the thermal treatment at 1273 K for 3 h, 86% of phosphate ion was recovered from an aqueous solution with 1.0 mmol L?1 of phosphate ion through the temperature swing between 303 and 373 K. The thermally treated activated carbon was reusable at least three times without any severe performance loss.
“The role of cobalt oxide or magnesium oxide in ozonation of ammonia nitrogen in water"
In this study, the reaction mechanisms for ozonation of ammonia nitrogen in the presence of Co3O4 or MgO were investigated. For the reaction over Co3O4, Cl- in the reaction solution was indispensable and ClO- was formed by a non-catalytic oxidation of Cl-. Co3O4 promoted the reaction of NH4+ with ClO- to give the products including NO3-, chloramines and gaseous products. In contrast, Cl- was unnecessary for the reaction with MgO. pH of the reaction solution was maintained at around 9 throughout the reaction owing to partial dissolution of MgO. Ammonia nitrogen was decomposed to mainly NO3- by non-catalytic radical reaction involving OH・, which was formed by the reaction of OH- with O3 in weakly basic solution. To keep the reaction solution weakly basic, H+ formed with the decomposition of NH4+ was neutralized. As a result, about the same amount of Mg2+ as that of decomposed ammonia nitrogen was dissolved.
“Catalytic reduction of nitrate in water over alumina-supported nickel catalyst toward purification of polluted groundwater"
Marina Kobune, Dai Takizawa, Jun Nojima, Ryoichi Otomo, Yuichi Kamiya
Pollution of groundwater with NO3- is a serious problem in the world. While catalytic reduction of NO3- over Pd-bimetallic catalysts including Cu-Pd and Sn-Pd is a promising method for purification of the groundwater, the use of precious metal is a major obstacle for practical applications. In the present study, we applied Ni/Al2O3 for the catalytic reduction of NO3- and compared the catalytic performance with that of unsupported Ni catalyst. The reaction rate over 5 wt.% Ni/Al2O3 was about 5 times higher than that of the unsupported Ni catalyst, based on unit weight of catalyst. While the unsupported Ni catalyst was completely deactivated in low partial pressure of H2 (= 0.75 atm) and high concentration of NO3- (= 800 ppm), Ni/Al2O3 was still active even under less reductive conditions ([NO3-]0 = 800 ppm and P(H2) = 0.5 atm). The unsupported Ni catalyst had the Ni0 particles formed by the reduction of NiO with H2 at 310 - 420 oC. On the other hand, 5 wt.% Ni/Al2O3 possessed the Ni0 particles formed from NiAl2O4 on Al2O3 by the reduction with H2 above 450 oC. It is plausible that those Ni0 particles had different properties, giving different catalytic properties. The Ni loadings for Ni/Al2O3 had a significant impact on the catalytic properties. The reaction orders with respect to both NO3- and H2 were 0.8 for 5 wt.% Ni/Al2O3, while those were 0 and -0.2, respectively, for 10 wt.% Ni/Al2O3. On 10 wt.% Ni/Al2O3, there were two kinds of the Ni0 particles, which were formed by low (310 - 420 oC) and high (450 oC ~) temperature H2 reductions. Unlike the Pd-bimetallic catalysts, the reduction of NO3- over Ni/Al2O3 did not proceed through NO2-.
“Magneli-Phase Titanium Suboxide Nanocrystals as Highly Active Catalysts for Selective Acetalization of Furfural"
Masanori Nagao, Sayaka Misu, Jun Hirayama, Ryoichi Otomo, Yuichi Kamiya
Alongside TiO2, Magneli-phase titanium suboxide having the composition of TinO2n-1 is a kind of attractive functional materials composed of titanium. However, there still remain problems to be overcome in the synthesis of titanium suboxide; the existing synthesis methods require high temperature typically over 1000 °C and/or postsynthesis purification. This study presents a novel approach to synthesis of titanium suboxide nanoparticles through solid-phase reaction of TiO2 with TiH2. Crystal phases of titanium suboxide were easily controlled by changing TiO2/TiH2 molar ratios in a TiO2-TiH2 mixed precursor, and a series of titanium suboxide nanoparticles including Ti2O3, Ti3O5, Ti4O7, and Ti8O15 were successfully obtained. The reaction of TiO2 with TiH2 proceeded at a relatively low temperature due to the high reactivity of TiH2, giving titanium suboxide nanoparticles without any postsynthesis purification. Ti2O3 nanoparticles and TiO2 were applied as solid acid catalysts for reaction of furfural with 2-propanol. Ti2O3 showed a high catalytic activity and high selectivity for acetalization of furfural, while TiO2 showed only poor activity for transfer hydrogenation of furfural. The difference in catalytic properties is discussed in terms of the acid properties of Ti2O3 and TiO2.
“A reliable method to create adjacent acid-base pair sites on silica through hydrolysis of pre-anchored amide" Editor’s Choice
Wontae Kim, Loida O. Casalme, Taiki Umezawa, Fuyuhiko Matsuda, Ryoichi Otomo, Yuichi Kamiya
A method to create adjacent acid-base pair sites, which are carboxyl and amino groups, respectively, on silica through hydrolysis of pre-anchored amide is proposed. This method can produce an adjacent acid-base pair sites. The catalyst showed excellent catalytic performance for aldol condensation of 4-nitrobenzaldehyde with acetone, overwhelming the catalyst having only amino group and an acid-base catalyst prepared in a conventional manner.
2020年度
令和2年度 高難度選択酸化反応研究会シンポジウム (令和3年1月22日(金), オンライン)
(依頼講演) 神谷 ”メタクロレイン選択酸化触媒の作用機構と新触媒開発”
触媒学会北海道支部講演会 (12月4日(金), オンライン)
(依頼講演) 神谷 ”硝酸塩で汚染された地下水を浄化するための触媒化学”
第36回ゼオライト研究発表会 (11月19日(木)〜20日(金), オンライン)
(口頭発表) 中村 ”濃厚ゲルを用いたHf-Betaの短時間合成およびそのルイス酸触媒特性”
International Symposium on Porous Materials 2020 (11月6日 (金)〜7日 (土), オンライン)
(口頭発表) 中村 ”Short-term synthesis of Hf-Beta zeolite from dense precursor gel”
(口頭発表) 黄淵 “Application of Water-resistant Metal-Organic Framework NH2-MIL-53(Al) as a Catalyst Support for Nitrite Reduction in Water”
