Catalytic performance of zinc containing ionic liquids immobilized on silica for the synthesis of cyclic carbonates

Cycloaddition of carbon dioxide and epoxides was investigated using zinc halide based Lewis acidic ionic liquids (ILs) as catalysts. ILs such as 1-butyl-3-methylimidazolium bromide (BMImBr), 1-butylpyridinium bromide (BPyBr), tetra-n-butylammonium bromide (TBABr) were mixed with zinc halide and supported on silica gel to produce heterogeneous catalysts. Catalytic reaction tests demonstrated that the incorporation of zinc ions can significantly enhance the catalytic activity of the silica-supported ILs for the cycloaddition of CO₂ to epoxides in solvent-free conditions. BPyBr-ZnCl₂/SiO₂ showed the highest propylene carbonate yield of 98% when the reaction was carried out with 0.5 g of catalyst at 120 °C at 1.89 MPa of CO₂ pressure for 4 h. The immobilized zinc containing IL catalyst could be reused for at least four cycles without any considerable loss of its activity.     

Metal Acetylacetonates as Highly Efficient and Cost Effective Catalysts for the Synthesis of Cyclic Carbonates from CO<Subscript>2</Subscript> and Epoxides

Abstract  

Metal acetylacetonates were found to be efficient and cost effective catalysts for the formation of cyclic carbonates by cycloaddition of carbon dioxide with epoxides, providing high to excellent yields of the corresponding carbonates. Among the various catalysts such as acetylacetonates of Co, Ni, Cu, Zn, Fe, Cr and VO studied, Ni(acac)₂ was found to be promising catalyst for this reaction. The present methodology was found to be superior due to the easy accessibility and comparatively inexpensive nature of metal acetylacetonates than salen complexes.     

Microwave-assisted,rapid cycloaddition of allyl glycidyl ether and CO2 by employing pyridinium-based ionic liquid catalysts

This study investigated the use of pyridinium-based ionic liquids (ILs) as an efficient catalyst for the rapid solvent-free microwave-assisted cycloaddition of allyl glycidyl ether (AGE) and CO₂ to yield allyl glycidyl carbonate (AGC) under moderate reaction conditions. The cycloaddition reaction occurred over a short reaction time of 30 s, resulting in a high turnover frequency (TOF) ranging from 200 to 7000 h^− 1. The effects of alkyl chain length and anion of pyridinium-based catalysts on the cycloaddition reactivity were studied. The effects of reaction parameters such as the amount of catalyst, microwave power, CO₂ pressure, and reaction time were also investigated.     

Cationic Polymers Bearing Quaternary Ammonium Groups-Catalyzed CO<Subscript>2</Subscript> Fixation with Epoxides

A series of cationic polymers containing quaternary ammonium groups turned out to be powerful catalysts for the CO₂-fixation of epoxides under an atmospheric pressure of CO₂ at elevated temperature. A variety of differently substituted aromatic and aliphatic epoxides were well tolerated and the polymeric catalysts could easily be recovered by a simple filtration and reused without any loss in catalytic activity.     

TiO<Subscript>2</Subscript>/Ni Inverse-Catalysts Prepared by Atomic Layer Deposition (ALD)

Abstract  

Atomic layer deposition (ALD) was used to deposit TiO₂ on Ni particles, and the catalytic activity of Ni for CO₂ reforming of methane (CRM) was evaluated. In the presence of TiO₂ islands on Ni surfaces, the onset temperature of the CRM reaction was lower than that of bare Ni. During the CRM reaction, carbon was deposited on the surface of bare Ni, which reduced the catalytic activity of the surface with time, and TiO₂ islands were able to remove carbon deposits from the surface. When the Ni surface was completely covered with TiO₂, the catalytic activity disappeared, demonstrating that tuning of the TiO₂ coverage on Ni is important to maximize the activity of the CRM reaction.     

Zirconium-based isoreticular metal-organic frameworks for CO<Subscript>2</Subscript> fixation via cyclic carbonate synthesis

Two highly stable isoreticular metal-organic frameworks comprising chains of zirconium coordinated with linkers of 1,4-H₂BDC (1,4-benzenedicarboxylic acid) and 4,4′-H₂BPDC (4,4′-biphenyldicarboxylic acid), denoted as MIL-140A and MIL-140C, were synthesized. The catalytic activity of these frameworks was studied for the coupling reaction of CO₂ and epoxides to produce cyclic carbonates under solvent-free conditions. Excellent activity was observed for both catalysts: they yielded high epoxide conversion with >99% selectivity toward the cyclic carbonate, and were fully reusable even after four cycles without any considerable loss of initial activity. The enhancement in the catalytic activity was explained based on acidity/basicity studies. The influence of various reaction parameters such as catalyst amount, reaction time, reaction temperature, and CO₂ pressure was also investigated. Reaction mechanism was proposed on the basis of experimental evidence and our previous DFT (density functional theory) studies.     

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>/Ce<Subscript>0.6</Subscript>Zr<Subscript>0.4</Subscript>O<Subscript>2</Subscript> Catalysts: Effect of Acidity and Basicity of the Catalysts

Abstract  

Ce _X Zr_1−X O₂ catalysts with different cerium content (X) (X = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0) were prepared by a sol–gel method for use in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Among these catalysts, Ce_0.6Zr_0.4O₂ was found to show the best catalytic performance. In order to enhance the acidity and basicity of Ce_0.6Zr_0.4O₂ catalyst, Ga₂O₃ was supported on Ce_0.6Zr_0.4O₂ (XGa₂O₃/Ce_0.6Zr_0.4O₂ (X = 1, 5, 10, and 15)) by an incipient wetness impregnation method with a variation of Ga₂O₃ content (X, wt%). Effect of acidity and basicity of Ga₂O₃/Ce_0.6Zr_0.4O₂ on the catalytic performance in the direct synthesis of dimethyl carbonate was investigated using NH₃-TPD and CO₂-TPD experiments. Experimental results revealed that both acidity and basicity of the catalysts played a key role in determining the catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Large acidity and basicity of the catalyst facilitated the formation of dimethyl carbonate. The amount of dimethyl carbonate produced over XGa₂O₃/Ce_0.6Zr_0.4O₂ catalysts increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, 5Ga₂O₃/Ce_0.6Zr_0.4O₂, which retained the largest acidity and basicity, showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.     

Microwave Assisted Synthesis of Cyclic Carbonate Using Homogeneous and Heterogeneous Ionic Liquid Catalysts

A comparative study was effectuated between the catalytic performance of homogeneous and silica supported ionic liquids (SSILs) for the cycloaddition of epoxides and CO₂ under microwave irradiation by varying the reaction parameters. Compared to the classical heating mode, both catalysts showed higher activity at moderate reaction condition through microwave irradiation.     

A Highly Selective Pd(OAc)<Subscript>2</Subscript>/Pyridine/K<Subscript>2</Subscript>CO<Subscript>3</Subscript> System for Oxidation of Terpenic Alcohols by Dioxygen

Abstract  

Molecular sieves, complex organic bases and radical oxidants are commonly used in alcohols oxidation reactions. In this work, we have evaluated the beneficial effects of addition of K₂CO₃ to Pd(II)-catalyzed oxidation alcohols, which resulted in a remarkable increase in the oxidation reaction rates without selectivity losses. Herein, in a metallic reoxidant-free system, terpenic alcohols (β-citronellol, nerol and geraniol) were selectively converted into respective aldehydes from Pd(II)-catalyzed oxidation reactions in presence of dioxygen. High conversions and selectivities (greater than 90%) were achieved in the presence of the Pd(OAc)₂/K₂CO₃ catalyst and pyridine excess. The exogenous role of others auxiliary anionic and nitrogen compounds was appraised.     

In Situ FT-IR Study of Diesel Hydrocarbon Oxidation Over Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst

Abstract  

The catalytic performance of Pt/Al₂O₃ for the total oxidation of a hydrocarbon mixture of n-decane and 1-methylnaphthalene was investigated by using in situ FT-IR spectroscopy. Although carbonate and/or carboxylate species were mainly detected under steady-state conditions, the formation of an acrylate species during the initial stage of the reaction was observed under transient conditions. Based on a comparison of the reaction and formation behavior of the acrylate species and CO₂ as a gaseous product, it was proposed that the total oxidation of the hydrocarbon mixture proceeds via the formation of an acrylate species as a reaction intermediate.     

Reductive amination of ethanol to ethylamines over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Ni(x)/Al₂O₃ (x=wt%) catalysts with Ni loadings of 5–25 wt% were prepared via a wet impregnation method on an γ-Al₂O₃ support and subsequently applied in the reductive amination of ethanol to ethylamines. Among the various catalysts prepared, Ni(10)/Al₂O₃ exhibited the highest metal dispersion and the smallest Ni particle size, resulting in the highest catalytic performance. To reveal the effects of reaction parameters, a reductive amination process was performed by varying the reaction temperature (T), weight hourly space velocity (WHSV), and NH₃ and H₂ partial pressures in the reactions. In addition, on/off experiments for NH₃ and H₂ were also carried out. In the absence of NH₃ in the reactant stream, the ethanol conversion and selectivities towards the different ethylamine products were significantly reduced, while the selectivity to ethylene was dominant due to the dehydration of ethanol. In contrast, in the absence of H₂, the selectivity to acetonitrile significantly increased due to dehydrogenation of the imine intermediate. Although a small amount of catalyst deactivation was observed in the conversion of ethanol up to 10 h on stream due to the formation of nickel nitride, the Ni(10)/Al₂O₃ catalyst exhibited stable catalytic performance over 90 h under the optimized reaction conditions (i.e., T=190 °C, WHSV=0.9 h^?1, and EtOH/NH₃/H₂ molar ratio=1/1/6).     

Ni-Co bimetallic catalyst for CH<Subscript>4</Subscript> reforming with CO<Subscript>2</Subscript>

A co-precipitation method was employed to prepare Ni/Al₂O₃-ZrO₂, Co/Al₂ O₃-ZrO₂ and Ni-Co/Al₂O₃-ZrO₂ catalysts. Their properties were characterized by N₂ adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO₂-TPD), and temperature-programmed surface reaction (CH₄-TPSR and CO₂-TPSR). Ni-Co/Al₂O₃-ZrO₂ bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO₂ adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO₂ adsorption sites (C + CO₂ = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH₄-CO₂-TPSR, there were 80.9% and 81.5% higher CH₄ and CO₂ conversion over Ni-Co/Al₂O₃-ZrO₂ catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al₂O₃-ZrO₂ catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support.     

CO and CO<Subscript>2</Subscript> methanation over Ni catalysts supported on alumina with different crystalline phases

The effect of alumina crystalline phases on CO and CO₂ methanation was investigated using alumina-supported Ni catalysts. Various crystalline phases, such as α-Al₂O₃, θ-Al₂O₃, δ-Al₂O₃, η-Al₂O₃, γ-Al₂O₃, and κ-Al₂O₃, were utilized to prepare alumina-supported Ni catalysts via wet impregnation. N₂ physisorption, H₂ chemisorption, temperature-programmed reduction with H₂, CO₂ chemisorption, temperature-programmed desorption of CO₂, and X-ray diffraction were employed to characterize the catalysts. The Ni/θ-Al₂O₃ catalyst showed the highest activity during both CO and CO₂ methanation at low temperatures. CO methanation catalytic activity appeared to be related to the number of Ni surface-active sites, as determined by H₂-chemisorption. During CO₂ methanation, Ni dispersion and the CO₂ adsorption site were found to influence catalytic activity. Selective CO methanation in the presence of excess CO₂ was performed over Ni/γ-Al₂O₃ and Ni/δ-Al₂O₃; these substrates proved more active for CO methanation than for CO₂ methanation.     

Oxidative reforming of methane on structured Ni-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts

The catalytic properties of Ni/Al₂O₃ composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6% CH₄, 2–9% O₂, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH₄, 6–12% CO₂, and 0–4% O₂, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O bond, and the phase composition of the catalyst. The structured Ni-Al₂O₃ catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal (Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La₂O₃, CeO₂) enhance the activity and stability of Ni-Al₂O₃/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming of methane on the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach a high methane conversion and does not exert any significant effect on the selectivity with respect to H₂.     

Photoreduction of Carbon Dioxide Over NaNbO<Subscript>3</Subscript> Nanostructured Photocatalysts

Abstract  

NaNbO₃ had been successfully developed as a new photocatalyst for CO₂ reduction. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet–visible spectroscopy (UV–Vis). The DFT calculations revealed that the top of VB consisted of the hybridized O 2p orbital, while the bottom of CB was constructed by Nb 3d orbital, respectively. In addition, the photocatalytic activities of the NaNbO₃ samples for reduction of CO₂ into methanol under UV light irradiation were investigated systematically. Compared with the bulk NaNbO₃ prepared by a solid state reaction method, the present NaNbO₃ nanowires exhibited a much higher photocatalytic activity for CH₄ production. This is the first example that CO₂ conversion into CH₄ proceeded on the semiconductor nanowire photocatalyst.     

Supported imidazole as heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO2

Imidazole anchored onto a silica matrix, by means of a propyl linkage, is found to be an effective heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO₂ in near quantitative yield. The versatility of this catalyst is demonstrated by using different substrates (epichlorohydrin, propylene oxide, butylene oxide and styrene oxide) for this cycloaddition reaction. These CO₂ insertion reactions were typically carried out in the temperature range of 343 to 403 K at 0.6 MPa CO₂ pressure under solvent-free conditions. Several spectroscopic methods were used to characterize the catalyst and study the integrity of the fresh and spent catalysts.     

Reduction of CO<Subscript>2</Subscript> to CO via reverse water-gas shift reaction over CeO<Subscript>2</Subscript> catalyst

CeO₂ catalysts with different structure were prepared by hard-template (Ce-HT), complex (Ce-CA), and precipitation methods (Ce-PC), and their performance in CO₂ reverse water gas shift (RWGS) reaction was investigated. The catalysts were characterized using XRD, TEM, BET, H₂-TPR, and in-situ XPS. The results indicated that the structure of CeO₂ catalysts was significantly affected by the preparation method. The porous structure and large specific surface area enhanced the catalytic activity of the studied CeO₂ catalysts. Oxygen vacancies as active sites were formed in the CeO₂ catalysts by H₂ reduction at 400 °C. The Ce-HT, Ce-CA, and Ce-PC catalysts have a 100% CO selectivity and CO₂ conversion at 580 °C was 15.9%, 9.3%, and 12.7%, respectively. The highest CO₂ RWGS reaction catalytic activity for the Ce-HT catalyst was related to the porous structure, large specific surface area (144.9 m²?g^?1) and formed abundant oxygen vacancies.     

Aqueous-Phase Hydrogenolysis of Glycerol to 1,3-propanediol Over Pt-H<Subscript>4</Subscript>SiW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript>

Abstract  

Hydrogenolysis of glycerol to 1,3-propanediol in aqueous-phase was investigated over Pt-H₄SiW₁₂O₄₀/SiO₂ bi-functional catalysts with different H₄SiW₁₂O₄₀ (HSiW) loading. Among them, Pt-15HSiW/SiO₂ showed superior performance due to the good dispersion of Pt and appropriate acidity. It is found that Br?nsted acid sites facilitate to produce 1,3-PDO selectively confirmed by Py-IR. The effects of weight hourly space velocity, reaction temperature and hydrogen pressure were also examined. The optimized Pt-HSiW/SiO₂ catalyst showed a 31.4% yield of 1,3-propanediol with glycerol conversion of 81.2% at 200 °C and 6 MPa.     

Biocompatible and recyclable amino acid binary catalyst for efficient chemical fixation of CO2

In this work, the cycloaddition reactions of CO₂ with various epoxides to form five-membered cyclic carbonates catalyzed by an efficient amino acid based biocompatible catalyst were investigated. It was found that the activity of amino acid could be obviously enhanced in the presence of alkali metal salts, and the l-tryptophan catalytic system was the most efficient among the catalysts employed. Based on the result, a possible mechanism for the synergetic effect of catalyst was proposed. The process reported here represents a simple, ecologically safer, cost-effective route to cyclic carbonates with high product quality, as well as easy catalyst recycling.     

Oxygen Isotope (<Superscript>18</Superscript>O<Subscript>2</Subscript>) Evidence on the Role of Oxygen in the Plasma-Driven Catalysis of VOC Oxidation

Abstract  

This paper reports isotopic evidence on nonthermal plasma-induced fixation of gas-phase oxygen on the surface of several catalysts such as TiO₂, Ag/TiO₂, Ag/γ-Al₂O₃ and Ag/MS-13X at atmospheric-pressure. On-line mass spectrometric analysis and stoichiometric comparison of reactants and products revealed that the fixed surface oxygen can be activated by nonthermal plasma. The fixed ¹⁸O by nonthermal plasma survived for a certain period of time (about 30 min), and involved in the formation of isotope-exchanged oxygen (¹⁸O¹⁶O) and isotope containing CO _x (CO and CO₂).