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Endothermic reactions

Yuanxing Wang, Cailing Niu, Dunwei Wang
How to effectively and efficiently reduce carbon dioxide (CO2 ) to value-added chemicals represent a frontier in catalysis research. Due to the high activation energy needs and the endothermic nature of CO2 reduction, the reactions are difficult to carry out. When H2 O is present, hydrogen evolution reactions (HER) often compete favorably with CO2 reduction reactions. For these reactions, catalysts are of critical importance to CO2 reduction. In this article, we review the various metal nanocatalysts for electrochemical CO2 reduction (ECR) reactions...
May 16, 2018: Journal of Colloid and Interface Science
Felix Schneck, Florian Schendzielorz, Nareh Hatami, Markus Finger, Christian Würtele, Sven Schneider
The endothermic reverse water-gas shift reaction (rWGS) for direct CO2 hydrogenation to CO is an attractive approach to carbon utilization. However, direct CO2 hydrogenation with molecular catalysts generally gives formic acid instead of CO as a result of the selectivity of CO2 insertion into M-H bonds. Based on the photochemical inversion of this selectivity, several synthetic pathways are presented for CO selective CO2 reduction with a nickel pincer platform including the first example of a photodriven rWGS cycle at ambient conditions...
May 17, 2018: Angewandte Chemie
Mengmeng Shao, Yangfan Shao, Wenzhou Chen, Kin Long Ao, Rui Tong, Qing Zhu, Iat Neng Chan, Weng Fai Ip, Xingqiang Shi, Hui Pan
Active catalysts for nitrogen fixation (N2-fixation) have been widely pursued through constant efforts for industrial applications. Here, we report a family of catalysts, MXenes (M2X: M = Mo, Ta, Ti, and W; X = C and N), for application in N2-fixation based on density functional theory calculations. We find that the catalytic performance of MXenes strongly depends on the reaction energy in each reaction step. More exothermic steps lead to higher catalytic performance in the course of N2-fixation. We show that the reaction energy in N2-fixation is strongly affected by the charge transfer: (1) if N atoms gain more electrons in a step, the reaction is exothermic with a larger reaction energy; (2) if N atoms lose electrons in a step, the reaction is endothermic in general...
May 16, 2018: Physical Chemistry Chemical Physics: PCCP
Kui Zhang, Tao Chen
Removal of IO3 - from environmental samples with low-cost methods and materials is very useful approach for especially large-scale applications. Corn stalk is highly abundant agriculture residual, which is employed as useful biosorbent in many studies. In the present work, dried powder of corn stalk is applied for the removal of IO3 - under various conditions. The results indicate that the Kd is 49.73 ml g-1 under general conditions (m/V = 8 g L-1 , t = 5 day, equilibrium pH = 7 ± 0...
May 11, 2018: Journal of Environmental Radioactivity
Hongyan Li, Pei Gao, Jianguo Cui, Feng Zhang, Fang Wang, Jici Cheng
Corncob activated carbon (CCAC) was prepared by a H3 PO4 activation method. The optimum conditions for the preparation of CCAC were determined by orthogonal experiments. The effects of pH, reaction time, CCAC dosage, and hexavalent chromium (Cr(VI)) concentrations on Cr(VI) removal by CCAC were studied. Corn straw activated carbon (CSAC) was also prepared using the optimum preparation conditions determined for CCAC. The properties of samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS)...
May 12, 2018: Environmental Science and Pollution Research International
Md Samrat Alam, Drew Gorman-Lewis, Ning Chen, Shannon L Flynn, Yong Ok, Kurt Konhauser, Daniel S Alessi
While numerous studies have investigated metal uptake from solution by biochar, few of these have developed a mechanistic understanding of the adsorption reactions that occur at the biochar surface. In this study, we explore a combined modeling and spectroscopic approaches for the first time to describe the molecular level adsorption of Ni(II) and Zn(II) to biochar using five types of biochar. Following thorough characterization, potentiometric titrations were carried out to measure the proton (H+) reactivity of each biochar, and the data was used to develop protonation models...
May 10, 2018: Environmental Science & Technology
Nor Fazila Khairudin, Mohd Farid Fahmi Sukri, Mehrnoush Khavarian, Abdul Rahman Mohamed
Dry reforming of methane (DRM) is one of the more promising methods for syngas (synthetic gas) production and co-utilization of methane and carbon dioxide, which are the main greenhouse gases. Magnesium is commonly applied in a Ni-based catalyst in DRM to improve catalyst performance and inhibit carbon deposition. The aim of this review is to gain better insight into recent developments on the use of Mg as a support or promoter for DRM catalysts. Its high basicity and high thermal stability make Mg suitable for introduction into the highly endothermic reaction of DRM...
2018: Beilstein Journal of Nanotechnology
Alexey L Kaledin, Darren M Driscoll, Diego Troya, Daniel L Collins-Wildman, Craig L Hill, John R Morris, Djamaladdin G Musaev
The impact of ambient gas molecules (X), NO2 , CO2 and SO2 on the structure, stability and decontamination activity of Cs8 Nb6 O19 polyoxometalate was studied computationally and experimentally. It was found that Cs8 Nb6 O19 absorbs these molecules more strongly than it adsorbs water and Sarin (GB) and that these interactions hinder nerve agent decontamination. The impacts of diamagnetic CO2 and SO2 molecules on polyoxoniobate Cs8 Nb6 O19 were fundamentally different from that of NO2 radical. At ambient temperatures, weak coordination of the first NO2 radical to Cs8 Nb6 O19 conferred partial radical character on the polyoxoniobate and promoted stronger coordination of the second NO2 adsorbent to form a stable diamagnetic Cs8 Nb6 O19 /(NO2 )2 species...
February 28, 2018: Chemical Science
Ting Yang, Mark E Hodson
Humic acid can effectively bind metals and is a promising adsorbent for remediation technologies. Our studies initially focussed on Cu2+ as a common aqueous contaminant. Previous studies indicate that carboxylic groups dominate Cu2+ binding to humic acid. We prepared a synthetic humic-like acid (SHLA) with a high COOH content using catechol (0.25 M) and glycine (0.25 M) with a MnO2 catalyst (2.5% w/v) at pH = 8 and 25 °C and investigated the adsorption behaviour of Cu2+ onto it. The SHLA exhibited a range of adsorption efficiencies (27%-99%) for Cu2+ depending on reaction conditions...
April 20, 2018: Science of the Total Environment
Hongxin Su, Weiwei Li, Yide Han, Ningning Liu
Magnetic carboxyl functional nanoporous polymer (MCFNP) was chemically fabricated by incorporation of magnetic Fe3 O4 precursor into the carboxyl functional nanoporous polymer (CFNP). The as-synthesized MCFNP was characterized and used as an adsorbent for rapid adsorption removal of methylene blue (MB) from wastewater. Several experimental parameters affecting the adsorption efficiency were investigated including initial pH, adsorbent dosage, initial MB concentration, contact time and temperature. The adsorption behavior of MCFNP displayed that adsorption kinetics and isotherms could be well fitted to the pseudo-second-order and Langmuir models, respectively...
April 25, 2018: Scientific Reports
Xing Chen, Xia Jiang, Wei Huang
Malodorous rivers are among the major environmental problems of cities in developing countries. In addition to the unpleasant smell, the sediments of such rivers can act as a sink for pollutants. The excessive amount of ammonia nitrogen (NH3 -N) in rivers is the main factor that causes the malodour. Therefore, a suitable method is necessary for sediment disposition and NH3 -N removal in malodorous rivers. The sediment in a malodorous river (PS) in Beijing, China was selected and modified via calcination (PS-D), Na+ doping (PS-Na) and calcination-Na+ doping (PS-DNa)...
March 2018: Royal Society Open Science
Brendan C Sweeny, Shaun G Ard, Nicholas S Shuman, Albert A Viggiano
The temperature-dependent kinetics for reactions of V+ , Fe+ , and Co+ with OCS are measured using a selected ion flow tube apparatus heated to 300 - 600 K. All three reactions proceed solely by C-S activation at thermal energies, resulting in metal sulfide cation formation. Previously calculated reaction pathways were employed to inform statistical modelling of these reactions for comparison to the data. As surmised previously, all three reactions at thermal energies require spin crossing, with the Fe+ reaction crossing once circumventing a prohibitive transition state, before crossing again to form ground state products...
April 2, 2018: Journal of Physical Chemistry. A
Letícia C D Lima, Daniela G C Peres, Adriano A Mendes
Commercial lipase from Thermomyces lanuginosus has been immobilized on glutaraldehyde-activated rice husk particles via covalent attachment. It was reached maximum immobilized protein concentration of 27.5 ± 1.8 mg g-1 of dry support using the initial protein loading of 40 mg g-1 of support. The immobilized biocatalyst was used to synthesize cetyl oleate (wax ester) via direct esterification of oleic acid and cetyl alcohol. The influence of relevant factors on ester synthesis, such as reaction temperature, biocatalyst concentration, presence or lack of hydrophobic organic solvents, acid:alcohol molar ratio, and reaction time has been evaluated...
March 24, 2018: Bioprocess and Biosystems Engineering
Haifeng Hu, Liu Yang, Zhen Lin, Xiaotong Xiang, Xiancai Jiang, Linxi Hou
A novel magnetic bioadsorbent beads composed of Fe3 O4 , chitosan, and Al(OH)3 (Fe3 O4 /CS/Al(OH)3 ) was synthesized by a modified solvothermal and in-situ reaction. The composite adsorbent was characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer, respectively. Adsorption toward F- onto Fe3 O4 /CS/Al(OH)3 was investigated as a function of Fe3 O4 concentration, initial solution pH, adsorbent dosage, initial fluorion concentration, co-existing ions in water and initial temperature...
March 20, 2018: International Journal of Biological Macromolecules
Zhi Su, Yu-Run Miao, Guanghui Zhang, Jeffrey T Miller, Kenneth S Suslick
The internal free volume of porous materials diminishes upon mechanical compression, and such volume collapse can have chemical consequences. We report here the endothermic bond breakage in a metal-organic framework (MOF) during compression-induced collapse. Upon bulk compression at 1.9 GPa, the effective number for Zr-O bonds between Zr(iv) ions and carboxylate groups in UiO-66 decreased from 4.0 to 1.9, as determined by EXAFS, and the internal free volume was synchronously collapsed. Consistent with the EXAFS data, IR spectra confirmed conversion of syn - syn bridging carboxylates to monodentate ligation, thus establishing mechanochemical reactions induced by external compression of MOFs...
December 1, 2017: Chemical Science
Mei-Fang Li, Yun-Guo Liu, Shao-Bo Liu, Guang-Ming Zeng, Xin-Jiang Hu, Xiao-Fei Tan, Lu-Hua Jiang, Ni Liu, Jun Wen, Xiang-Hui Liu
Adsorption of tetracycline (TC) and ciprofloxacin (CIP) in single and binary systems by diethylenetriaminepentaacetic acid-functionalized magnetic graphene oxide (DDMGO) was explored. DDMGO were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. The adsorption kinetics and equilibrium data of single antibiotic were well fitted by pseudo-second-order and Freundlich isotherm models, respectively...
March 2, 2018: Journal of Colloid and Interface Science
Misagh Ghobadi, Mahdi Gharabaghi, Hadi Abdollahi, Zohreh Boroumand, Marzieh Moradian
In recent decades, considerable amounts of rare earth elements have been used and then released into industrial wastewater, which caused serious environmental problems. In this work, in order to recycle rare earth cations (La3+ and Ce3+ ) from aqueous solutions, MnFe2 O4 -Graphene oxide magnetic nanoparticles were synthesized and after characterization studies, their adsorption isotherms, kinetics, thermodynamics and desorption were comprehensively investigated. Characterized was performed using XRD, FE-SEM, FT-IR, Raman spectroscopy, VSM, BET and DLS...
March 8, 2018: Journal of Hazardous Materials
Prajakta Rajaram Parab, K Alexander Heufer, Ravi Xavier Fernandes
Isopentanol is a potential next-generation biofuel for future applications to Homogeneous Charge Compression Ignition (HCCI) engine concepts. To provide insights into the combustion behavior of isopentanol, especially to its auto-ignition behavior which is linked both to efficiency and pollutant formation in real combustion systems, detailed quantum chemical studies for crucial reactions are desired. H-Abstraction reaction rates from fuel molecules are key initiation steps for chain branching required for auto-ignition...
April 25, 2018: Physical Chemistry Chemical Physics: PCCP
A M Nasir, P S Goh, A F Ismail
A novel hydrous iron-nickel-manganese (HINM) trimetal oxide was successfully fabricated using oxidation and coprecipitation method for metalloid arsenite removal. The atomic ratio of Fe:Ni:Mn for this adsorbent is 3:2:1. HINM adsorbent was identified as an amorphous nanosized adsorbent with particle size ranged from 30 nm to 60 nm meanwhile the total active surface area and pore diameter of HINM area of 195.78 m2 /g and 2.43 nm, respectively. Experimental data of arsenite adsorption is best fitted into pseudo-second order and Freundlich isotherm model...
June 2018: Chemosphere
Farheen Khan, Rizwan Wahab, Mohamed Essam Hagar, Rua Alnoman, Mohd Rashid
The present work describes the synthesis of copper oxide nanoparticles (CuONPs) via a solution process with the aim of applying the nano-adsorbent for the reduction of methylene blue (MB) dye in alkaline media. These NPs were characterized via Field emission scanning electron microscopy (FE-SEM), X-ray diffraction, high-resolution Transmission electron microscopy (TEM), and ultra violet UV-visible spectroscopy to confirm their morphology and crystalline and optical properties in order to design an adsorption-degradation process...
February 27, 2018: Nanomaterials
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