Ionic liquid-assisted preparation of hydroxyapatite and its catalytic performance for decarboxylation of itaconic acid

The synthesis of methacrylic acid from biomass-derived itaconic acid is a green route,for it can get rid of the dependence on fossil resource.In order to solve the problems on this route such as use of a preciousmetal catalyst and a corrosive homogeneous alkali,we prepared a series of hydroxyapatite catalysts by an ionic liquid-assisted hydrothermal method and evaluated their catalytic performance.The results showed that the ionic liquid[Bmim]BF_(4) can affect the crystal growth of hydroxyapatite,provide fluoride ion for fluorination of hydroxyapatite,and adjust the surface acidity and basicity,morphology,textural properties,crystallinity,and composition of hydroxyapatite.The[Bmim]BF4 dosage and hydrothermal temperature can affect the fluoride ion concentration in the hydrothermal system,thus changing the degree of fluoridation of hydroxyapatite.High fluoride-ion concentration can lead to the formation of CaF_(2) and thus significantly decrease the catalytic performance of hydroxyapatite.The hydrothermal time mainly affects the growth of hydroxyapatite crystals on the c axis,leading to different catalytic performance.The suitable conditions for the preparation of this fluoridized hydroxyapatite are as follows:a mass ratio of[Bmim]BF4 to calcium salt=0.2:1,a hydrothermal time of 12 h,and a hydrothermal temperature of 130℃.A maximal methacrylic acid yield of 54.7%was obtained using the fluoridized hydroxyapatite under relatively mild reaction conditions(250℃ and 2 MPa of N_(2))in the absence of a precious-metal catalyst and a corrosive homogeneous alkali.

Influence of Ca/P ratio on the catalytic performance of hydroxyapatite for decarboxylation of itaconic acid to methacrylic acid

Methacrylic acid,an important organic chemical,is commercially manufactured starting from fossil feedstock.The decarboxylation of itaconic acid derived for biomass is a green route to the synthesis of methacrylic acid.In view of the problems existing in the researches on this route such as use of noble metal catalyst,harsh reaction conditions and low desired-product yield,we prepared a series of hydroxyapatite catalysts with different Ca/P molar ratios and evaluated their catalytic performance.The results showed that the hydroxyapatite catalyst with a Ca/P molar ratio of 1.58 had the best catalytic activity.The highest yield of MAA up to 61.2%was achieved with basically complete conversion of itaconic acid under the suitable reaction conditions of 1 equivalent of NaOH,2 MPa of N_(2),250℃,and 2 h.On this basis,a reaction network for the decarboxylation of itaconic acid to methacrylic acid catalyzed by hydroxyapatite was established.With the aid of catalyst characterization using X-ray powder diffraction,NH3/CO2 temperature-programmed desorption,N_(2)physisorption,inductively coupled plasma optical emission spectrometry,and scanning electron microscopy,we found that the distribution of surface acid sites and basic sites,crystal growth orientation,texture properties and morphology of hydroxyapatite varied with the Ca/P molar ratio.Furthermore,the change of the crystal growth orientation and its influence on the surface acidity and alkalinity were clarified.

High catalytic performance of CuCe/Ti for CO oxidation and the role of TiO_(2)

CuCe/Ti-A and CuCe/Ti-R catalysts were prepared using anatase TiO_(2)(TiO_(2)-A)and rutile TiO_(2)(TiO_(2)-R)as supports using the incipient wetness impregnation method for the carbon monoxide(CO)oxidation reaction and were compared with a CuCe-C catalyst prepared using the co-precipitation method.The CuCe/Ti-A catalyst exhibited the highest activity,with complete CO conversion at 90℃,when the gas hourly space velocity was 24000 ml.g^(-1).h^(-1) and the CO concentration was approximately 1%(vol).A series of characterizations of the catalysts revealed that the CuCe/Ti-A catalyst has a larger specific surface area,more Cu+species and oxygen vacancies,and the Cu species of CuCe/Ti-A catalyst is more readily reduced.In situ FT-IR results indicate that the bicarbonate species generated on the CuCe/Ti-A catalyst have lower thermal stability than the carbonate species on CuCe/Ti-R,and will decompose more readily to form CO_(2).Therefore,CuCe/Ti-A has excellent catalytic activity for CO oxidation.

Preparation and characterization of H_4SiW_(12)O_(40)@MIL-100(Fe) and its catalytic performance for synthesis of 4,4'-MDA

The catalytic performance of co mmonly used heteropolyacids （H3PW12O40, H4SiW12O40 and H3PMO12O40 synthesis of 4,4＇-methylenedianiline （4,4＇-MDA） from aniline and formaldehyde was evaluated and the result showed that H4SiW12O40 with moderate acid strength exhibited the best catalytic performance. Then HaSiW12O40@MIL-100（Fe） was prepared by encapsulating H4SiW12O40 within the pores of MIL-100（Fe） to facilitate its recovery and reuse. The prepared H4SiW12O40@MIL-100（Fe） was characterized by means of FT-IR, N2 adsorption-desorption, XRD, TG and then the catalytic performance was evaluated. The result showed that H4SiW12O40 was highly dispersed in the pores of MIL-100（Fe）, and both the Keggin structure of HaSiW12O40 and the crystal skeleton structure of MIL-100（Fe） could be effectively/preserved. Furthermore, H4SiW12O40@ MIL-100（Fe） showed excellent catalytic performance under the following reaction conditions： a molar ratio of aniline to formaldehyde = 5, a mass ratio of catalyst to formaldehyde = 1.2, a reaction temperature of 120 ℃ and a reaction time of 6 h. Under the above reaction conditions, the conversion of aniline was 41.1%, and the yield and selectivity of 4,4＇-MDA were 81,6% and 79.2%, respectively. Unfortunately, an appreciable loss in the catalytic activity of the recovered H4SiW12O40@MIL-100（Fe） was observed because of the blocking of the pores and the change of the acidity resulted from the adsorption of alkaline organics such as aniline and 4,4＇-MDA. The adsorbed alkaline organics could be cleaned up when the recovered catalyst was washed by methanol and DMF. Then the catalyst was effectively reused up to three cycles without much loss in its activity.

A core–shell Ni/SiO_(2)@TiO_(2) catalyst for highly selective one-step synthesis of 2-propylheptanol from n-pentanal

One-step synthesis of 2-propylheptanol(2-PH)from n-pentanal via a reaction integration of n-pentanal self-condensation and successive hydrogenation is of great significance for it can simplify process flow and reduce energy consumption.The key to promotion of 2-PH selectivity is to enhance the competitiveness of n-pentanal self-condensation with respect to its direct hydrogenation.For this purpose,a core–shell structured Ni/SiO_(2)@TiO_(2) catalyst was designed and prepared.With the precise architecture of this core–shell structured catalyst,n-pentanal can be firstly in contact with TiO_(2) to 2-propyl-2-heptenal(2-PHEA)while the direct hydrogenation to n-pentanol can be effectively inhibited,and then 2-PHEA diffuses into the core of Ni/SiO_(2) and is hydrogenated to 2-PH.The spatial threshold of the core–shell catalyst significantly enhanced its catalytic performance;a 2-PH selectivity of 77.9%was reached with a 100%npentanal conversion.The 2-PH selectivity is much higher than that obtained by employing Ni/TiO_(2) catalyst.Furthermore,the reaction kinetics of one-step synthesis of 2-PH from n-pentanal catalyzed by Ni/SiO_(2)@TiO_(2) was studied and its kinetic model was established which is useful for reactor design and scale-up.

Chitosan-catalyzed n-butyraldehyde self-condensation reaction mechanism and kinetics

The chitosan was found to possess an excellent catalytic performance in n-butyraldehyde selfcondensation to 2 E2 H.Under suitable conditions,the conversion of n-butyraldehyde,the yield and selectivity of 2 E2 H separately attained 96.0%,86.0%and 89.6%.The chitosan catalyst could be recovered and used for 5 times without a significant deactivation after being treated with ammonium hydroxide.In order to elucidate the reaction mechanism,the adsorption and desorption of n-butyraldehyde on the surface of chitosan were studied using in situ FT-IR spectroscopy analysis.The result showed that n-butyraldehyde interacts with\\NH2 group of chitosan to form an intermediate species with an enamine structure.Then the reaction process of n-butyraldehyde self-condensation was monitored by React-IR technique and it was found that n-butyraldehyde self-condensation to 2-ethyl-3-hydroxyhexanal followed by a dehydration reaction to 2-ethyl-2-hexenal.On this basis,chitosan-catalyzed n-butyraldehyde self-condensation reaction mechanism was speculated and its reaction kinetics was investigated.The self-condensation reaction follows auto-catalytic reaction characteristics and then the corresponding kinetic model was established.

Synthesis and Characterization of Novel Bronsted-Lewis Acidic Ionic Liquids

To meet the demands of some kinds of reactions catalyzed simultaneously by Br?nsted acid and Lewis acid catalyst, two novel Br?nsted-Lewis acidic ionic liquids, 1-carboxyethylene-3-(4-zinc acetate sulfobutyl) imidazolium chloride ([CH3COO-Zn-O3S-bim-CH2CH2COOH]Cl) and 1-(1,2-dicarboxy) ethylene-3-(4-zinc acetate sulfobutyl) imidazolium chloride ([CH3COO-Zn-O3S-bim-C4H5O4]Cl) were synthesized, in which both Br?nsted and Lewis acidic sites existed in the cation. The structures of the ionic liquids were determined by means of FT-IR, 1H NMR and elemental analysis. The results of Py-IR analysis indicated that the two novel ionic liquids have both Br?nsted and Lewis acid properties. The acid strength values (H0) of the ionic liquids were measured utilizing the UV-visible spectroscopy combined with Hammett indicator method, and the acid amount of them was determined by acid-base titration.

Synthesis of magnetic Pb/Fe_(3)O_(4)/SiO_(2) and its catalytic activity for propylene carbonate synthesis via urea and 1,2-propylene glycol

To facilitate the recovery of Pb/SiO_(2) catalyst,magnetic Pb/Fe_(3)O_(4)/SiO_(2) samples were prepared separately by emulsification,sol-gel and incipient impregnation methods.The catalyst samples were characterized by means of X-ray diffraction and N_(2) adsorption-desorption,and their catalytic activity was investigated in the reaction for synthesizing propylene carbonate from urea and 1,2-propylene glycol.When the gelatin was applied in the preparation of Fe_(3)O_(4) at 60℃ and the pH value was controlled at 4 in the preparation of Fe_(3)O_(4)/SiO_(2),the Pb/Fe_(3)O_(4)/SiO_(2) sample shows good catalytic activity and magnetism.Under the reaction conditions of a reaction temperature of 180℃,reaction time of 2h,catalyst percentage of 1.7 wt-% and a molar ratio of urea to PG of 1∶4,the yield of propylene carbonate attained was 87.7%.