Solar Syngas Production From H2O and CO2 via Two Step Thermochemical Cycles Based on FeO/Fe3O4 Redox Reactions: Kinetic Analysis

2010 ◽  
Author(s):  
Anastasia Stamatiou ◽  
Peter G. Loutzenhiser ◽  
Aldo Steinfeld
Keyword(s):  
Redox Reactions ◽  
Active Sites ◽  
Thermochemical Cycle ◽  
Thermochemical Cycles ◽  
Simultaneous Reduction ◽  
Syngas Production ◽  
Diffusion Controlled ◽  
Shrinking Core ◽  
Arrhenius Kinetic Parameters ◽  
Reduction Of Co2

Syngas production via a two-step H2O/CO2-splitting thermochemical cycle based on FeO/Fe3O4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of Fe3O4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO2 and H2O with FeO to CO and H2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with FeO in the range 973–1273 K and CO2/H2O concentrations of 15–75%. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir-Hinshelwood type was formulated to describe the competitiveness of the reaction based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.

Thermodynamic Analysis of CO2 Reduction in the SnO2/SnO Solar Thermochemical Cycle

2011 ◽  
Author(s):  
Evgeny Shafirovich ◽  
Allen Garcia
Keyword(s):  
Redox Reactions ◽  
Co2 Reduction ◽  
Co2 Concentration ◽  
Thermochemical Cycle ◽  
Co2 Utilization ◽  
Thermochemical Cycles ◽  
Global Problems ◽  
Petroleum Resources ◽  
Chemical Products ◽  
Solar Thermochemical

CO2 utilization for the production of valuable chemical products may help mitigate two global problems: increasing CO2 concentration in the atmosphere and depleting petroleum resources. Solar thermochemical cycles for CO2 splitting provide relatively high efficiencies of solar energy conversion while operating at realistic temperatures. In the present paper, the cycles proposed previously are reviewed and a novel cycle, based on SnO2/SnO redox reactions, is proposed. The results of thermodynamic calculations for the CO2 reduction step in this cycle are reported.

scholarly journals Adsorption and Photocatalytic Reduction of Carbon Dioxide on TiO2

Catalysts ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 47
Author(s):  
Oleksandr Shtyka ◽  
Viktar Shatsila ◽  
Radoslaw Ciesielski ◽  
Adam Kedziora ◽  
Waldemar Maniukiewicz ◽  
...  
Keyword(s):  
Photocatalytic Activity ◽  
Active Sites ◽  
High Efficiency ◽  
Chemical Potential ◽  
Band Gap Energy ◽  
Electromagnetic Spectrum ◽  
Reaction Intermediates ◽  
Factors Affecting ◽  
Phase Reduction ◽  
Reduction Of Co2

The photocatalytic activity of TiO2 depends on numerous factors, such as the chemical potential of electrons, charge transport properties, band-gap energy, and concentration of surface-active sites. A lot of research has been dedicated to determining the properties that have the most significant influence on the photocatalytic activity of semiconductors. Here, we demonstrated that the activity of TiO2 in the gas-phase reduction of CO2 is governed mainly by the desorption rate of the reaction intermediates and final products. This indicates that the specific surface area of TiO2 and binding strength of reaction intermediates and products are the main factors affecting the photocatalytic activity of TiO2 in the investigated process. Additionally, it was shown that rutile exhibits higher photocatalytic activity than anatase/rutile mixtures mainly due to its high efficiency in the visible portion of the electromagnetic spectrum.

Molecular Dynamic Simulation of Hydrogen Production by Catalytic Gasification of Key Intermediates of Biomass in Supercritical Water

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Hui Jin ◽  
Bin Chen ◽  
Xiao Zhao ◽  
Changqing Cao
Keyword(s):  
Supercritical Water ◽  
Active Sites ◽  
Density Functional ◽  
Free Carbon ◽  
Ni Catalyst ◽  
Catalytic Gasification ◽  
Syngas Production ◽  
Reactor Optimization ◽  
Cu Catalyst ◽  
Microscopic Reaction

Supercritical water gasification (SCWG) is an efficient and clean conversion of biomass due to the unique chemical and physical properties. Anthracene and furfural are the key intermediates in SCWG, and their microscopic reaction mechanism in supercritical water may provide information for reactor optimization and selection of optimal operating condition. Density functional theory (DFT) and reactive empirical force fields (ReaxFF) were combined to investigate the molecular dynamics of catalytic gasification of anthracene and furfural. The simulation results showed that Cu and Ni obviously increased the production of H radicals, therefore the substance SCWG process. Ni catalyst decreased the production of H2 with the residence time of 500 ps while significantly increased CO production and finally increased the syngas production. Ni catalyst was proved to decrease the free carbon production to prohibit the carbon deposition on the surface of active sites; meanwhile, Cu catalyst increased the production of free carbon.

Solar Syngas Production via H2O/CO2-Splitting Thermochemical Cycles with Zn/ZnO and FeO/Fe3O4Redox Reactions†

2010 ◽  
Vol 22 (3) ◽  
pp. 851-859 ◽  
Author(s):  
A. Stamatiou ◽  
P. G. Loutzenhiser ◽  
A. Steinfeld
Keyword(s):  
Thermochemical Cycles ◽  
Syngas Production

CO2 Splitting in a Hot-Wall Aerosol Reactor via the Two-Step Zn/ZnO Solar Thermochemical Cycle

2009 ◽  
Author(s):  
Peter G. Loutzenhiser ◽  
M. Elena Ga´lvez ◽  
Illias Hischier ◽  
Anastasia Stamatiou ◽  
Aldo Steinfeld
Keyword(s):  
Flow Reactor ◽  
Energy Conversion Efficiency ◽  
Solar Furnace ◽  
Thermochemical Cycle ◽  
X Ray Diffraction ◽  
Concentrated Solar Energy ◽  
High Temperature Process ◽  
Solar Thermochemical ◽  
Reduction Of Co2

Using concentrated solar energy as the source of high-temperature process heat, a two-step CO2 splitting thermochemical cycle based on Zn/ZnO redox reactions is applied to produce renewable carbon-neutral fuels. The solar thermochemical cycle consists of: 1) the solar endothermic dissociation of ZnO to Zn and O2; 2) the non-solar exothermic reduction of CO2 with Zn to CO and ZnO; the latter is the recycled to the 1st solar step. The net reaction is CO2 = CO + 1/2 O2, with products formed in different steps, thereby eliminating the need for their separation. A Second-Law thermodynamic analysis indicates a maximum solar-to-chemical energy conversion efficiency of 39% for a solar concentration ratio of 5000 suns. The technical feasibility of the first step of the cycle has been demonstrated in a high-flux solar furnace with a 10 kW solar reactor prototype. The second step of the cycle is experimentally investigated in a hot-wall quartz aerosol flow reactor, designed for in-situ quenching of Zn(g), formation of Zn nanoparticles, and oxidation with CO2. The effect of varying the molar flow ratios of the reactants was investigated. Chemical conversions were determined by gas chromatography and X-ray diffraction. Chemical conversions of Zn to ZnO of up to 88% were obtained for a residence time of ∼ 3.05 s. For all of the experiments, the reactions primarily occurred outside the aerosol jet flow on the surfaces of the reaction zone.

scholarly journals Bacterial leaching kinetics for copper dissolution from a lowgrade Indian chalcopyrite ore

2013 ◽  
Vol 66 (2) ◽  
pp. 245-250 ◽  
Author(s):  
Abhilash ◽  
K.D. Mehta ◽  
B.D. Pandey
Keyword(s):  
Phase Identification ◽  
Low Grade ◽  
Bacterial Leaching ◽  
Copper Dissolution ◽  
Diffusion Controlled ◽  
Shrinking Core ◽  
Copper Mines ◽  
Chalcopyrite Ore ◽  
Best Fit

Bio-leaching of copper (0.3%) from a low grade Indian chalcopyrite ore of Malanjkhand copper mines, using a native mesophilic isolate predominantly Acidithiobacillus ferrooxidans (A.ferrooxidans), is reported. A bio-recovery of 72% Cu was recorded in the presence of this culture (not adapted), which increased to 75% with an ore adapted culture after 35 days at 35ºC and pH 2.0 with <50fim particles. The kinetic data showed best fit for the diffusion-controlled shrinking core model, exhibiting linear plots for [1- 2/3X-(1-X)2/3] vs time (X-fraction leached). Apparently, the role of the bacteria is to convert the ferrous ion to the ferric state, which oxidizes the chalcopyrite in order to dissolve copper, while maintaining a high redox potential. The activation energy value (E) was calculated to be 96 and 108 kJ/mol for the un-adapted culture and the ore adapted culture respectively in the temperature range 25-35ºC. This leaching mechanism was corroborated by XRD phase identification and SEM studies of the leach residue.

scholarly journals Dynamic Structural Changes in Nickel Single-Atom Catalysts During Electrochemical Reduction of CO2 to CO

2021 ◽  
Author(s):  
Bingbao Mei ◽  
Changzhi Ai ◽  
Lushan Ma ◽  
Cong Liu ◽  
Shuai Yang ◽  
...  
Keyword(s):  
Active Sites ◽  
Structural Changes ◽  
Theoretical Calculations ◽  
Reduction Reaction ◽  
Single Atom ◽  
Structure Evolution ◽  
Potential Range ◽  
Dynamic Configuration ◽  
Carbon Abatement ◽  
Reduction Of Co2

Abstract Electrochemical CO2 reduction reaction (ECO2RR) is an important route for global carbon abatement. However, a comprehensive picture of the structure evolution of metal active sites is currently lacked in ECO2RR. Here, we present the first full view of Ni single-atom catalyst for ECO2RR over a broad potential range. Comprehensive X-ray absorption spectroscopy (XAS) analyses confirmed the Ni coordinated with pyrrole nitrogen in the form of Ni-N4 attached with an axial O2 ligand. Operando XAS revealed the precise structure of the Ni single-atom catalyst that dynamically changes with the shift of applied potentials. Such changes ultimately contributed to the CO selectivity variation ranging from 20%-99%. Interestingly, the Ni center was found to move toward the N4 plane during the ECO2RR, which played a crucial role of reaching near-unity CO selectivity. Together with theoretical calculations, a clear quantitative correlation between the dynamic configuration and the catalytic properties was established.

scholarly journals Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM

2021 ◽  
Author(s):  
Xing Huang ◽  
Travis Jones ◽  
Alexey Fedorov ◽  
Ramzi Farra ◽  
Christophe Copéret ◽  
...  
Keyword(s):  
Gas Phase ◽  
Structural Dynamics ◽  
Redox Reactions ◽  
Active Sites ◽  
Chemical Potential ◽  
Hydrogen Oxidation ◽  
Simultaneous Detection ◽  
Metal Catalysts ◽  
Operating Conditions ◽  
Chemical Dynamics

<div>Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown and assignments of active sites remain speculative. Herein, we present an operando transmission electron microscopy study that interrelates structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, we reveal how the interaction between metal and surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium towards a state controlled by chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structureactivity insights that identify distinct mechanisms for water formation and reveals the means by which the system self-adjusts to changes of the gas phase chemical potential. Density function theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis. <br></div>

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