Comparison of catalytic pyrolysis of biomass with MCM-41 and CaO catalysts by using TGA–FTIR analysis

Pyrolysis of corncob with and without catalyst was investigated using thermogravimetry analyzer coupled with Fourier transform infrared spectroscopy (TGA–FTIR). The effects of two completely different catalysts, acid catalyst (MCM-41) and base catalyst (CaO), on the formation characteristics and composition of pyrolysis vapor were studied. The results show that these two catalysts give different product distributions. For catalytic run with MCM-41, the molality of carbonyl compounds decreases 10.2%, while that of phenols, hydrocarbons and CH₄ increases 15.32%, 4.29% and 10.16% compared with non-catalytic run, respectively. The increase of phenols exhibits in a wide temperature range from about 295 °C to 790 °C in the catalytic run with MCM-41 catalyst. However, the use of CaO in pyrolysis of corncob leads to a huge change of product distribution. The molality of acids decreases 75.88%, while the molality of hydrocarbons and CH₄ increases 19.83% and 51.05% compared with non-catalytic run, respectively. CaO is very effective in deacidification and the conversion of acids promotes the formation of hydrocarbons and CH₄. Catalytic pyrolysis of corncob with CaO shows two main weight-loss stages. The first stage is from 235 °C to 310 °C with a weight loss of 31%. The second stage is from 650 °C to 800 °C with a weight loss of 21%.     

Thermal stability of Ti–MCM-41

Ti containing mesoporous MCM-41 materials have been synthesized through two methods: heating and non-heating [room temperature (RT)]. The synthesized materials have been characterized using X-ray diffraction, Fourier transform infrared, nitrogen sorption, and X-ray fluorescence methods and their thermal stabilities evaluated using thermogravimetric methods in inert atmosphere. The thermal stabilities have been analyzed based on the synthesis method, as well as on the amount of titanium in the MCM-41 materials. The thermal stability results suggest that uncalcined MCM-41 materials generally show higher mass loss than their calcined counterparts. Also, the RT-synthesized materials showed lower stability than the high-temperature synthesized samples for the uncalcined samples. It is also been found that MCM-41 materials show improved thermal stabilities as the amount of titanium is increased.     

beta-peptides as catalysts: poly-beta-leucine as a catalyst for the Juliá-Colonna asymmetric epoxidation of enones

Poly-beta-leucines have been evaluated as catalysts for the Juliá-Colonna asymmetric epoxidation of enones; the beta 3-isomer was found to be an effective catalyst for the epoxidation of chalcone (70% ee) and some analogues.     

Preparation,characterization, and hydrogenation activity of new Rh0–MCM-41 catalysts prepared from as-synthesized MCM-41 and RhCl3

Impregnation of as-synthesized MCM-41 silica by ethanolic solutions of rhodium(III) chloride was tested as an alternative to its introduction into the synthesis gel to get, after calcination and reduction by H₂, highly dispersed metal(0) nanoparticles throughout the mesopores network. Rh(III) and Rh(0)–based solids thus obtained were analyzed by infrared spectroscopy, elemental analysis, transmission electron microscopy, N₂ sorption, and X-ray diffraction. Materials with 1.6 wt % of rhodium could be obtained as a result of CTA⁺/Rh³⁺ exchange. The determining role of CTA⁺ was emphasized through blank experiments. In a second series of materials, ethanol was also exploited for its ability to reduce Rh(III). All Rh(0)-based solids were tested as catalysts in the hydrogenation of styrene under mild temperature and pressure conditions. Catalysis performances of the most efficient sample (reduced by H₂) were further compared with those of a very similar material prepared by the introduction of Rh(III) directly into the synthesis gel of MCM-41 silica. Better cis selectivities in the hydrogenation of disubstituted arene derivatives were achieved with materials issued from the new preparation method.     

Cobalt imine–pyridine–carbonyl complex functionalized metal–organic frameworks as catalysts for alkene epoxidation

Aerobic epoxidation of alkene is a green and economical route to produce epoxides. For such reaction, transition metal complexes exhibit favorable catalytic activity. In this work, NH₂-MIL-101, a stable metal–organic framework (MOF) material with large surface area and high pore volume, was functionalized with pyridine-2,6-dicarbaldehyde and Co(NO₃)₂, to realize the immobilization of Co(II) via imine–pyridine–carbonyl (N,N,O) tridentate ligands bonding to MOF skeleton. The modified materials were applied as heterogeneous catalysts for the aerobic epoxidation of cyclohexene at ambient temperature, and multiple factors were studied to explore their influences on catalytic effects. Under the optimal reaction conditions, satisfactory substrate conversion and epoxide selectivity were reached. In addition, this catalytic system is suitable for a variety of alkene substrates. Furthermore, recycle experiments and infrared spectroscopy characterization illustrated that the coordination surroundings of Co are altering smoothly during the reaction process, thus having an impact on the performance of catalyst.

     

Chiral model complexes for methane monooxygenase and their asymmetric catalysis of styrene epoxidation

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Platinum–tin complexes as catalysts for the anodic oxidation of borohydride

Platinum–tin complexes were prepared by the reduction of Pt(IV) with Sn(II) in HCl media and studied by light absorption spectrometry, X-ray photoelectron spectroscopy (XPS), and electron microscopy. The formation of three complexes, H₃[Pt(SnCl₃)₅], H₂[Pt(SnCl₃)₂Cl₂], and H₂[Pt₃(SnCl₃)₈], depending on HCl and SnCl₂ concentrations, has been shown. The glassy carbon (GC) electrode modified in the complexes solutions was found to be an electrocatalyst for borohydride oxidation in a 1.0-M NaOH solution. Comparison of BH₄ ⁻ electrooxidation on Pt and on GC modified with platinum–tin complexes has shown that catalytic hydrolysis of BH₄ ⁻ did not proceed in the latter case in contrast to its oxidation on the Pt electrode, and only direct BH₄ ⁻ oxidation has been observed in the positive potentials scan. The activity of Pt–Sn complexes for BH₄ ⁻ oxidation changes with time and eventually decreases due to Sn(II), bound in the complex with Pt(II), oxidation by atmospheric oxygen. The complexes may be renewed by addition of missing amounts of SnCl₂ and HCl.     

Chiral mesoporous templated silicas as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

New mesoporous templated silicas of the MCM-41 family covalently linked to chiral ephedrine are used as heterogeneous chiral auxiliaries in the enantioselective alkylation of benzaldehyde by diethylzinc. Promising results are obtained with these inorganic–organic catalysts. Various factors which may affect the activity, selectivity and enantioselectivity are studied. Comparison with homogeneous catalysis is carried out.     

Performance of C1-symmetric chiral ammonium betaines as catalysts for the enantioselective Mannich-type reaction of α-nitrocarboxylates

The catalytic performance of C₁-symmetric chiral ammonium betaines in the enantioselective direct Mannich-type reaction of α-nitrocarboxylates with N-Boc imines has been investigated. The most effective catalyst structure has been identified; this provides a reliable synthetic route to a variety of enantiomerically enriched α-tetrasubstituted α,β-diamino acid derivatives.     

A new series of chiral catalysts for the enantioselective borane reduction of ketones

A new series of 1,3,2-oxazaborolidine catalysts substituted in position 4 by the (CH3)3C(CH2)n group (n=2, 3, 4, 5) were synthesized and applied to the borane reduction of prochi-ral ketones. The relationship between catalyst structure and enantioselectivity was discussed.     

Improved catalytic performance of nitrided Co–Ti and Fe–Ti catalysts for oxygen reduction as non-noble metal cathodes in acidic media

M–Ti/carbon black electrocatalysts (M: Mn, Fe, Co, Ni, Cu, Mo) were prepared by the polymerized complex (PC) method and subsequent nitridation under ammonia flow, and were investigated as cathodes for the oxygen reduction reaction (ORR) in 0.1 M H₂SO₄ aq. Among the metals investigated, Co and Fe gave high onset potentials of 0.86 and 0.87 V vs. RHE, respectively. In comparison with the Co-only catalyst, the Co–Ti catalyst showed higher current, reflecting high density of Co-related active sites. The presence of Ti was also essential for the electrode stability under severe acidic and oxidizing conditions.     

The properties of gold catalysts precursors adsorbed on the MCM-41 materials modified with Mn and Fe oxides

Silica mesoporous materials modified with manganese and iron were obtained by the hydrothermal method. Gold was introduced to pure and modified silica materials by the direct hydrothermal and impregnation methods. Nitrogen adsorption/desorption studies evidenced formation of the materials with large total surface area and mesoporous structure. Unmodified silica materials showed regular pore arrangement. The uniform porous structure was distorted in the iron or manganese containing samples. XRD, UV-Vis/DRS spectroscopy and temperature programmed reduction studies revealed changes of the nature of transition metal oxide and gold species on the different preparation stages. The oxide species after drying were strongly dispersed and partially incorporated to the silica framework. High temperature treatment led to the formation of extraframework Mn and Fe oxide species. Complex processes of gold deposition were observed during hydrothermal synthesis and impregnation of modified silica materials. The increase of the size of gold species was observed during calcination. The presence of transition metal oxides decreased sintering of gold crystallites.     

Cyclic seleninate esters as catalysts for the oxidation of sulfides to sulfoxides, epoxidation of alkenes, and conversion of enamines to α-hydroxyketones

Cyclic seleninate esters serve as catalysts for the rapid oxidation of sulfides to sulfoxides, alkenes to epoxides, and enamines to α-hydroxyketones. Optimal conditions were found that minimize the overoxidation of the product sulfoxides to sulfones and the hydrolysis of epoxides to diols. In some examples such as styrene derivatives, oxidative cleavage was observed instead of epoxidation. The enamine oxidations proceed via the initial formation of dimeric 2,5-diamino-1,4-dioxane species, which were hydrolyzed in situ to the final products. The structure of one such dimer was confirmed by X-ray crystallography.     

Ionic liquids as phase transfer catalysts: Enhancing the biphasic extractive epoxidation reaction for the selective synthesis of β-O-glycosides

Ionic liquids promoted the direct epoxidation of glycals acting as PTC. 1,2-anhydrosugars were prepared by the oxidation of glycals under biphasic conditions with dimethydioxirane generated in situ from oxone/acetone and amphiphilic IL’s as catalysts. β-O-glycosides were synthesized in good yields by the nucleophilic ring opening of epoxy carbohydrate derivatives. Also, 3,4,6-benzyl protected carbohydrates and β-N-glycosides could be prepare by this method.     

Preparation of enantiomerically pure p-substituted phenylethyl hydroperoxides by kinetic resolution and their use as enantioselective oxidants in the asymmetric Weitz–Scheffer epoxidation of E-chalcone

The kinetic resolution of a variety of secondary para-substituted phenylethyl hydroperoxides by Raphanus sativus L. (black radish peroxidase) in the presence of guaiacol is reported. The peroxidase enzyme recognized (R)-configured alkyl aryl hydroperoxides, which furnished optically active (S)-hydroperoxides and (R)-alcohols. Kinetic resolution of tertiary hydroperoxides by the enzyme was unsuccessful. This study also shows how the optically active p-substituted (S)-hydroperoxides obtained can be employed as enantioselective oxidants in the asymmetric Weitz–Scheffer epoxidation of E-chalcone in the presence of KF-Al₂O₃ as a base. In all cases, a chalcone epoxide with the (αS,βR)-configuration was obtained as the major isomer. Under the optimized reaction conditions, the enantiomeric excess of the chalcone epoxide was obtained in up to 49% in CH₃CN at ?40 °C.     

Chiral β- and γ-aminoalcohols derived from (+)-camphor and (−)-fenchone as catalysts for the enantioselective addition of diethylzinc to benzaldehyde

The addition of Me₃SiCN and LiCH₂CN to (+)-camphor and (−)-fenchone, respectively, followed by reduction leads to chiral β- and γ-aminoalcohols. The enantioselectivities realized using these aminoalcohols as ligands in the addition of Et₂Zn to benzaldehyde were lower than those obtained using the corresponding δ-aminoalcohols.     

Self-supported BINOL-Zn catalysts for heterogeneous enantioselective epoxidation of (E)-α,β-unsaturated ketones

A class of chiral self-supported catalysts prepared from bis-BINOL ligands and diethyl zinc were successfully applied in the hetereogeneous enantioselective epoxidation of a range of (E)-α,β-unsaturated ketones, affording the corresponding epoxy ketones in high enantioselectivity. The self-supported catalysts were easily recovered from the reaction mixture and were reusable for several consecutive runs.     

Factors affecting the efficiency of hybrid chiral mesoporous silicas used as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

Chiral hybrid organic–inorganic materials were prepared by anchoring optically active β-aminoalcohols such as (−)-ephedrine on MCM-41 type silica as a member of micelle-templated silicas (MTS). Silylation of the surface was performed with halogenopropyltrimethoxysilane. Then, (−)-ephedrine was anchored through halogen substitution. These materials were used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the various factors such as accessibility to the catalytic sites and coverage of the inorganic surface, which affect their efficiency (activity, selectivity and enantioselectivity).