Ferrosilicate-Based Heterogeneous Fenton Catalysts: Influence of Crystallinity, Porosity, and Iron Speciation

Different ferrosilicate samples have been prepared with varying degrees of crystallinity, porous texture, and speciation of the Fe sites by both hydrothermal and sol–gel procedures: Fe-silicalite-1 with microcrystals (2–10 µm) and nanocrystals (180 nm), Fe-containing composite material consisting of silicalite-1 and amorphous silica, and two samples of mesoporous Fe-containing amorphous silica Fe–SiO2. The resulting solids have been tested for their potential as organic pollutants removal under Fenton-like conditions in heterogeneous catalytic wet peroxide oxidation of phenol and clarithromycin lactobionate. Our results indicate that the three aforementioned parameters show a strong interplay towards the abatement of pollutants in liquid phase. Thus, samples with high crystallinity show an improved performance in the oxidation of organic contaminants over amorphous samples in which the Fe speciation is very well controlled.The work was financially supported by the Ministry of Education and Science of the Russian Federation (RFMEFI60417 X 0159, title of the agreement: “Development of methods for hydrotreating of vacuum residue into high-quality marine fuels on macroporous catalysts”). The authors from Spanish side thank the Spanish Ministry of Economy and Competitiveness (MINECO), Generalitat Valenciana and FEDER (CTQ2015-66080-R MINECO/FEDER and PROMETEOII/2014/010) for financial support. J.G.A. thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for his fellowship (BES-2013-063678)

One-step solvent-free synthesis of cyclic carbonates by oxidative carboxylation of styrenes over a recyclable Ti-containing catalyst

A mesoporous titanium-silicate prepared by evaporation-induced self-assembly is an efficient heterogeneous catalyst for the one-step oxidative carboxylation of styrenes with tert-butyl hydroperoxide and carbon dioxide in the presence of tetrabutylammonium bromide as cocatalyst under mild solvent-free conditions (50–70 °C, 8 bar CO2). The selectivity to cyclic carbonates reaches 69–70% at 92–98.5% substrate conversion. The catalyst can be easily recovered by filtration and reused several times without a significant deterioration of the catalytic performance. The volume yield of SC as high as 1.1 kg/L could be achieved after seven reuses

One-step solvent-free synthesis of cyclic carbonates by oxidative carboxylation of styrenes over a recyclable Ti-containing catalyst

A mesoporous titanium-silicate prepared by evaporation-induced self-assembly is an efficient heterogeneous catalyst for the one-step oxidative carboxylation of styrenes with tert-butyl hydroperoxide and carbon dioxide in the presence of tetrabutylammonium bromide as cocatalyst under mild solvent-free conditions (50–70 °C, 8 bar CO2). The selectivity to cyclic carbonates reaches 69–70% at 92–98.5% substrate conversion. The catalyst can be easily recovered by filtration and reused several times without a significant deterioration of the catalytic performance. The volume yield of SC as high as 1.1 kg/L could be achieved after seven reuses

Development of Solid Acid Catalysts Based on Sibunit Carbon Material for Cellulose Transformation into 5-hydroxymethilfurfural

Твердые кислотные катализаторы для одностадийного процесса получения 5-гидроксиметилфурфурола (5-ГМФ) из целлюлозы приготовлены на основе графитоподобного углеродного материала «Сибунит-4» методами окисления и последовательного окисления и сульфирования. Образцы окисленного сибунита получали путем окисления водными растворами азотной кислоты или влажной воздушной смесью. Для получения окисленных- сульфированных образцов окисленные угли сульфировали в дымящейся серной кислоте при 200 °С. Катализаторы исследовали методами низкотемпературной адсорбции азота, кислотно- основного титрования NaOH и испытывали в одностадийном процессе гидролиза-дегидратации мехактивированной целлюлозы в гидротермальных условиях при 180 °С. Общее содержание кислотных групп (сульфо-, карбоксильных, лактонных и фенольных) для окисленных образцов сопоставимо, а для окисленных-сульфированных превышает в 1,5-2 раза количество кислотных групп сибунита, сульфированного при 200 °С. Активность катализаторов сопоставима с образцами, сульфированными при 150 и 200 °С. Выходы 5-ГМФ и глюкозы варьируются в пределах 17-20 и 38-42 % соответственноSolid acid catalysts based on graphite-like carbon material “Sibunit-4” have been developed to be utilized in the one-pot process of 5-hydroxymethylfurfural production from cellulose using oxidation and subsequent oxidation-sulfonation methods. The samples of oxidized carbon have been produced via oxidation of the carbon’s surface by water solutions of nitric acid or by wet air mixture; for oxidizedsulfonated samples to be produced oxidized carbons have been additionally sulfonated in fuming sulfuric acid at 200 °С. The catalysts developed have been investigated by methods of low-temperature nitrogen absorption and titration with NaOH and also tasted in the one-pot hydrolysis-dehydration of mechanically activated cellulose under hydrothermal conditions of 180 °С. The total amount of acidic groups (sulfo, carboxyl, lactone, and phenolic) for oxidized samples is comparable and for the oxidized-sulfonated is 1.5-2 times higher than the amount of acid groups in the sibunit sulfonated at 200 ° C. The activity of the catalysts with respect to sulfonated samples at 150 ° C and 200 ° C is comparable. The yields of 5-HMF and glucose ranges of 17-20% and 38-42%, respectivel

Hydrogen Production by N-Heterocycle Dehydrogenation over Pd Supported on Aerogel-Prepared Mg-Al Oxides

Tetradecahydrophenazine (14HP) is a nitrogen-containing heterocycle compound with a high content of hydrogen that can be released during its dehydrogenation to phenazine (P). The high stability of the 14HP/P pair and relatively low dehydrogenation temperature make 14HP a promising organic hydrogen carrier. This manuscript is devoted to the investigation of hydrogen production by 14HP dehydrogenation over Pd supported on a series of magnesium-aluminum oxides prepared by the aerogel method. This technique made it possible to synthesize catalyst supports characterized by a high surface area and high concentration of surface active sites where active transition metals could be stabilized in a finely dispersed state. The synthesized aerogels had high specific surface areas and pore volumes. A surface area as high as 600 m2/g after calcination at 500 °C was observed for the mixed aerogel with an Mg:Al ratio of 1:4. An increase in the concentration of acidic electron-acceptor sites determined by EPR on the surface of the mixed magnesium-aluminum oxide supports with a high surface area prepared by the aerogel method was found to result in higher hydrogen production due to the faster dehydrogenation of sterically hindered nitrogen-containing tetradecahydrophenazine heterocycles

Hydrogen Production by N-Heterocycle Dehydrogenation over Pd Supported on Aerogel-Prepared Mg-Al Oxides

Tetradecahydrophenazine (14HP) is a nitrogen-containing heterocycle compound with a high content of hydrogen that can be released during its dehydrogenation to phenazine (P). The high stability of the 14HP/P pair and relatively low dehydrogenation temperature make 14HP a promising organic hydrogen carrier. This manuscript is devoted to the investigation of hydrogen production by 14HP dehydrogenation over Pd supported on a series of magnesium-aluminum oxides prepared by the aerogel method. This technique made it possible to synthesize catalyst supports characterized by a high surface area and high concentration of surface active sites where active transition metals could be stabilized in a finely dispersed state. The synthesized aerogels had high specific surface areas and pore volumes. A surface area as high as 600 m2/g after calcination at 500 °C was observed for the mixed aerogel with an Mg:Al ratio of 1:4. An increase in the concentration of acidic electron-acceptor sites determined by EPR on the surface of the mixed magnesium-aluminum oxide supports with a high surface area prepared by the aerogel method was found to result in higher hydrogen production due to the faster dehydrogenation of sterically hindered nitrogen-containing tetradecahydrophenazine heterocycles

Development of Solid Acid Catalysts Based on Sibunit Carbon Material for Cellulose Transformation into 5-hydroxymethilfurfural

Твердые кислотные катализаторы для одностадийного процесса получения 5-гидроксиметилфурфурола (5-ГМФ) из целлюлозы приготовлены на основе графитоподобного углеродного материала «Сибунит-4» методами окисления и последовательного окисления и сульфирования. Образцы окисленного сибунита получали путем окисления водными растворами азотной кислоты или влажной воздушной смесью. Для получения окисленных- сульфированных образцов окисленные угли сульфировали в дымящейся серной кислоте при 200 °С. Катализаторы исследовали методами низкотемпературной адсорбции азота, кислотно- основного титрования NaOH и испытывали в одностадийном процессе гидролиза-дегидратации мехактивированной целлюлозы в гидротермальных условиях при 180 °С. Общее содержание кислотных групп (сульфо-, карбоксильных, лактонных и фенольных) для окисленных образцов сопоставимо, а для окисленных-сульфированных превышает в 1,5-2 раза количество кислотных групп сибунита, сульфированного при 200 °С. Активность катализаторов сопоставима с образцами, сульфированными при 150 и 200 °С. Выходы 5-ГМФ и глюкозы варьируются в пределах 17-20 и 38-42 % соответственноSolid acid catalysts based on graphite-like carbon material “Sibunit-4” have been developed to be utilized in the one-pot process of 5-hydroxymethylfurfural production from cellulose using oxidation and subsequent oxidation-sulfonation methods. The samples of oxidized carbon have been produced via oxidation of the carbon’s surface by water solutions of nitric acid or by wet air mixture; for oxidizedsulfonated samples to be produced oxidized carbons have been additionally sulfonated in fuming sulfuric acid at 200 °С. The catalysts developed have been investigated by methods of low-temperature nitrogen absorption and titration with NaOH and also tasted in the one-pot hydrolysis-dehydration of mechanically activated cellulose under hydrothermal conditions of 180 °С. The total amount of acidic groups (sulfo, carboxyl, lactone, and phenolic) for oxidized samples is comparable and for the oxidized-sulfonated is 1.5-2 times higher than the amount of acid groups in the sibunit sulfonated at 200 ° C. The activity of the catalysts with respect to sulfonated samples at 150 ° C and 200 ° C is comparable. The yields of 5-HMF and glucose ranges of 17-20% and 38-42%, respectivel

Carbonized Melamine Cyanurate as a Palladium Catalyst Support for the Dehydrogenation of N-heterocyclic Compounds in LOHC Technology

In this work, the use of graphite-like carbon nitride (g-C3N4) with improved texture characteristics for the synthesis of supported palladium catalysts of dehydrogenation of nitrogen-containing heterocycles was studied. This process is key to the creation of liquid organic carrier technology (LOHC) using N-heterocycles as reversibly hydrogenated/dehydrogenated substrates. For the preparation of graphite-like carbon nitride supports with advanced textural characteristics, well-established technology of the melamine cyanurate complex carbonization and standard techniques of adsorption precipitation together with wet impregnation were used for the synthesis of Pd-containing systems. The activity of the synthesized catalysts was studied in decahydroquinoline dehydrogenation. The high weight content of extractable hydrogen (7.2 wt%) and the high extraction rate, respectively, make it possible to consider these substances as the most promising N-heterocyclic compounds for this technology. It was shown that an increase in the specific surface area of g-C3N4 allows for achieving a slightly lower but comparable fineness of palladium particles for the 1 wt% Pd/MCA-500 sample, compared to the standard 1 wt% Pd/C. In this case, the catalytic activity of 1 wt% Pd/MCA-500 in the dehydrogenation of both substrates exceeded the analogous parameter for catalysts supported by nitrogen-free supports. This regularity is presumably associated with the electron-donor effect of surface nitrogen, which favorably affects the dehydrogenation rate as well as the stability of catalytic systems

Effect of Pretreatment with Acids on the N-Functionalization of Carbon Nanofibers Using Melamine

Nowadays, N-functionalized carbon nanomaterials attract a growing interest. The use of melamine as a functionalizing agent looks prospective from environmental and cost points of view. Moreover, the melamine molecule contains a high amount of nitrogen with an atomic ratio C/N of 1/2. In present work, the initial carbon nanofibers (CNFs) were synthesized via catalytic pyrolysis of ethylene over microdispersed Ni–Cu alloy. The CNF materials were pretreated with 12% hydrochloric acid or with a mixture of concentrated nitric and sulfuric acids, which allowed etching of the metals from the fibers and oxidizing of the fibers’ surface. Finally, the CNFs were N-functionalized via their impregnation with a melamine solution and thermolysis in an inert atmosphere. According to the microscopic data, the initial structure of the CNFs remained the same after the pretreatment and post-functionalization procedures. At the same time, the surface of the N-functionalized CNFs became more defective. The textural properties of the materials were also affected. In the case of the oxidative treatment with a mixture of acids, the highest content of the surface oxygen of 11.8% was registered by X-ray photoelectron spectroscopy. The amount of nitrogen introduced during the post-functionalization of CNFs with melamine increased from 1.4 to 4.3%. Along with this, the surface oxygen concentration diminished to 6.4%

Development of Sulfonated Catalysts Based on Graphite-Like Carbon Sibunit for Cellulose Hydrolysis

Твердые кислотные катализаторы, предназначенные для переработки целлюлозы в востребованные химические соединения (глюкозу и 5-гидроксиметилфурфурол) в водной среде, готовили на основе графитоподобного углеродного материала «Сибунит-4» методом сульфирования дымящейся серной кислотой при различных температурах с последующей обработкой в воде при 180 ºС. Катализаторы исследованы методами низкотемпературной адсорбции азота, кислотно-основного титрования. Изучение активности катализаторов в процессе гидролиза механически активированной микрокристаллической целлюлозы проводили при 180 °С и 1 МРа в инертной атмосфере. Основными продуктами процесса являются глюкоза и 5-гидроксиметилфурфурол с максимальными выходами до 46 и 22 %. Сравнение результатов исследования активности и устойчивости катализаторов показало, что наиболее перспективным является катализатор, сульфированный при 200 °СSolid acidic catalysts for the processing of cellulose in the value-added chemical (glucose and 5-hydroxymethylfurfural) in aqueous media ware prepared on the basis of graphite-like carbon «Sibunit - 4» using sulfonation by sulfuric acid at different temperatures, followed by treatment in water at 180 ºC. Prepared catalysts were characterized by low-temperature nitrogen adsorption and acid-base titration. Testing of catalytic activity in the hydrolysis of the mechanically activated microcrystalline cellulose was carried out at 180 ° C and 1 MPa of argon. The main products of the process are glucose and 5-hydroxymethylfurfural with yields up to 46 and 22 mol. %. Comparison of the results of the activity and stability of catalysts showed that the most promising is the catalyst sulfated at 200 °