ZrO2 nanotube arrays were prepared by the anodization method in a mixture of formamide and glycerol (volume ratio = 1:1) containing 1 wt% NH4F and 1 wt% H2O. The catalysts were obtained through the impregnation of zirconia nanotubes with zirconium sulfate aqueous solution followed by calcinating in air at high temperature. The morphology and structure of the nanotubes and catalysts were characterized through scanning electron microscopy, X-ray diffraction, and infrared spectra analysis. Various factors that affect the catalytic activity were investigated in detail. An esterification conversion percentage of 97.6% was achieved for the catalyst prepared with zirconia supports which were pretreated at 500 °C, followed by loading 65% Zr(SO4)2 and calcinating at 400 °C.
Authors:Zuguang Liu, Taishun Zhang, Wei Zeng, Hualong Zhu, and Xinnan An
Cationic polymerization of α-pinene with silicotungstic acid (SiW12) as a catalyst was investigated. The structure of polymers and the catalysts were characterized by FT-IR, 1H-NMR and GPC. The experiments show that SiW12 is more active than both phosphotungstic acid and phosphomolybdic acid. The protons dissociating from the catalysts are the reactive species. SiW12 is found to be both the polymerization initiator and the counter-anion of the growing cationic center. The polymerization conditions are optimized by the single factor method as follows: monomer concentration is 50% (v/v), the dosage of catalysts is 7 wt% referred to α-pinene, reaction temperature is 50 °C, reaction time is 1 h. Under these conditions, the overall conversion of α-pinene is up to 90.87%, the polymer yield is 62.46% and its average number molecular weight is about 600. GC–MS analysis shows that there are six isomers of α-pinene after the reaction, but their content is very low. Most of α-pinene are changed to poly(α-pinene).
Authors:Yanxiang Liu, Xujie Lu, Feng Wu, and Nansheng Deng
The adsorption and photodegradation behavior of tetracycline (TC), chloramphenicol (CAP) and sulfamethoxazole (SMX) in clay mineral dispersion was investigated in this work. Only TC showed significant adsorption to natural montmorillonite and rectorite, whereas CAP and SMX adsorbed to natural montmorillonite, kaolinite and rectorite to a much lower extent. The adsorption equilibrium constants (L/kg) of TC to natural montmorillonite were 332 and 108 at pH 3.0 and 7.0, respectively. The kinetic rate constant kapp (min−1) for the removal of CAP in the presence of different clay minerals follows the sequence: montmorillonite KSF (1.6 × 10−2) > rectorite (4.6 × 10−3) > natural montmorillonite (3.8 × 10−3) > kaolinite (2.8 × 10−3). Removal of SMX follows the same sequence. Oxalate significantly promotes the removal of CAP and SMX in montmorillonite KSF dispersion, while penicillamine (PEN) and β-cyclodextrin retard the diminution. After 3 h of irradiation in 5 g/L KSF dispersion, the total organic carbon was reduced by 72 and 39% for CAP and SMX, respectively.
In this study, UV/oxidant and UV/TiO2/oxidant systems were employed to treat textile wastewater. The parent compound was C.I. reactive red 198 (RR198). The selected oxidants were H2O2, Na2S2O8, NaBrO3, and NaIO4. The effects of oxidant dosage (1–24 mM), wavelength of UV (254 and 365 nm) and radical scavenger addition (C2H5OH) were determined in UV/oxidant systems. The experimental results revealed that all oxidants effectively decolorized RR198 under 254 nm irradiation; however, only Na2S2O8 and NaIO4 can decolorize RR198 under 365 nm irradiation. The decolorization rates fit a pseudo-first order reaction model. Under 254 nm irradiation and 6 mM oxidant addition, the decolorization rate constants (k) of H2O2, Na2S2O8, NaBrO3, and NaIO4 for RR198 were 10.24, 17.93, 13.37, and 11.90 h−1. Under 365 nm irradiation, 1 g/L TiO2 and 1 mM NaIO4 addition, the k values of the UV/TiO2, UV/NaIO4, and UV/TiO2/NaIO4 systems were 0.50, 0.52, and 11.67 h−1. The inhibition of RR198 decolorization by the addition ethanol indicates that the primary decolorization pathway involves hydroxyl radicals in UV/H2O2 and UV/Na2S2O8 systems, and that oxidation by other radicals is probably important in UV/NaBrO3 and UV/NaIO4 systems.
Authors:E. Gucciardi, V. Chiodo, S. Freni, S. Cavallaro, A. Galvagno, and J. C. J. Bart
Catalytic reactions of the steam reforming (SR) of dimethyl ether (DME) and (bio)ethanol to hydrogen-rich gas were compared in a fixed-bed continuous-flow reactor at temperatures of 550–650 °C under atmospheric pressure over Rh/Al2O3 catalysts in terms of product distribution. Rh/Al2O3 catalysts are able to catalyze the high-temperature SR of both EtOH and DME, but in the latter case, higher H2 yields are obtained and the catalyst is less prone to coking. The aim of this work is to optimise the hydrogen production. Differences in reaction pathways over DME/H2O and EtOH/H2O are indicated.
A carbon-based solid acid catalyst is prepared by incomplete carbonization of sulfonated naphthalene and used for the hydrolysis of carboxylic acid esters. XRD, FT-IR, TGA and acid density test are employed to characterize the structure and performance of the catalysts. The results show that the catalysts prepared under different synthesis temperature and time are amorphous carbon composed of small aromatic carbon sheets with –SO3H groups. The catalytic activities of catalysts for methyl acetate hydrolysis are closely related with their acid densities. The appropriate synthesis temperature and time for the catalyst are 230 °C and 12 h and the acid density of catalyst under the optimized conditions can reach 4.49 mmol g−1. The carbon-based solid acid shows higher catalytic activity than Amberlyst-15 resin as a popular hydrolysis catalyst for a series of carboxylic acid esters hydrolysis. The catalyst has good thermal stability, which can bear 250 °C without decomposition. It also remains satisfactory catalytic activity for methyl acetate hydrolysis after six times recycling.
Authors:Liying Song, Kaixiang Li, Xiaohong Li, and Peng Wu
Ordered Ru-containing mesoporous polymers/silica (xRu-MPS) was for the first time successfully synthesized via a one-pot method. Characterization results demonstrated that the xRu-MPS samples had ordered meso-structure and Ru nanoparticles were highly dispersed on/inside the mesoporous polymer/silica. The xRu-MPS catalysts were proved to be efficient for the hydrogenation of benzaldehyde and its derivatives. When the Ru loading reached up to 4.8 wt%, the conversion of benzaldehyde could arrive 96% with 97% selectivity to benzyl alcohol. The 4.8Ru-MPS catalyst can also catalyze the hydrogenation of a series of benzaldehyde derivatives with different substituents at the phenyl ring with high performance. The results are quite comparable with those obtained on mesopolymer supported Ru catalyst prepared by a traditional impregnation method.
Authors:Dan Liu, Jianzhou Gui, Jianfeng Ding, JuanJuan Ma, Juyoung Lee, and Zhaolin Sun
Deep removal of dibenzothiophene from model diesel under mild conditions (323 K) by oxidation with H2O2 was studied, using Na2WO4·2H2O in a halogen-free ionic liquid. The removal of DBT could reach 99.4% and the sulfur content would be reduced from initial 500 to 3 μg/g, which can meet the standards of ultra-deep desulfurization. The model diesel after oxidation could be easily separated by simple decantation, demonstrated an effective and simple separation method. This catalytic system can be recycled five times without significant change on desulfurization results. The mechanism of the catalytic oxidation process was also proposed, a new ionic liquid-peroxytungstate complex was generated as the active species for supplying the active oxygen for desulfurization reaction.
Authors:Everton Fernando Zanoelo and Cristina Benincá
The oxidation of 5-O-caffeoylquinic acid (5-CQA) was investigated in the temperature range from 161 to 188 °C. The kinetic experiments were carried out in small batch reactors made of glass, where a very thin (1.1 μm) fixed bed of powder 5-CQA was in contact with air at approximately 91.4 kPa. Aqueous 5-CQA solutions were prepared with the solid found in the reactors at different reaction times and used to measure the decrease of 5-CQA concentrations with a spectrophotometer operated at 323 nm. A shrinking core model was applied to describe the non-catalytic heterogeneous reaction between 5-CQA and oxygen. It basically assumes mass transfer of O2 from bulk air to the outer surface of nonporous particles of solid 5-CQA, where an irreversible reaction with no formation of solid products takes place. The proposed model correctly reproduced the obtained kinetic results in all the investigated operating conditions when an exponential reduction of external area of solid with reaction time was taken into account. Arrhenius-type expressions successfully described the dependence of the calculated global reaction and shrinking rate constants on temperature. An activation energy close to 77046 J mol−1 was found for the slow combustion reaction of 5-CQA.
Authors:Valeria Palermo, Ángel G. Sathicq, Patricia G. Vázquez, Horacio J. Thomas, and Gustavo P. Romanelli
In this research, we report the preparation of doped PMo Keggin heteropolyacids where Mo is partially replaced by V, Bi, and Bi–V. These catalysts were characterized by means of ICP-AES analysis, 31P-NMR, UV–visible spectra, FT-IR spectra, thermal analysis, and textural properties. In addition, the activities of the synthesized catalysts were evaluated in the selective oxidation of sulfides to sulfoxides/sulfones. The incorporation of V, Bi and Bi–V into the structure of H3PMo12O40 increases the catalytic activity. The two most active catalysts, those with V and V–Bi were supported on aminopropyl-functionalized silica (SiO2NH2) and they were found to be and efficient heterogeneous catalysts for the selective oxidation of diphenylsulfide to the corresponding sulfoxide/sulfone.