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>

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>

Heterogeneous catalysts for gas-phase conversion of ethylene to higher olefins

2018 ◽  
Vol 34 (5) ◽  
pp. 595-655 ◽  
Author(s):  
Mohammad Ghashghaee
Keyword(s):  
Gas Phase ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Supply And Demand ◽  
Value Added ◽  
Direct Conversion ◽  
Operating Conditions ◽  
Light Olefins ◽  
Phase Conversion ◽  
Natural Gas Reservoirs

Abstract The reduced availability of propylene and C4 products from steam crackers continues to provoke on-purpose technologies for light olefins such that almost 30% of propylene in 2025 is predicted to be supplied from unconventional sources. Furthermore, the recent discoveries of natural gas reservoirs have urged interest in the conversion of surplus alkanes and alkenes, especially ethane and ethylene. The direct conversion of ethylene to propylene or a combination of value-added chemicals, including butylenes and oligomers in the range of gasoline and diesel fuel, provides the capability of responding to the fluctuations in the balance between supply and demand of the main petrochemicals. A comprehensive review of heterogeneous catalysts for the gas-phase conversion pathways is presented here in terms of catalytic performances (ethylene conversion and product selectivities), productivities, lifetimes, active sites, physicochemical properties, mechanisms, influence of operating conditions, deactivation and some unresolved/less-advanced aspects of the field. The addressed catalysts cover both zeolitic materials and transition metals, such as tungsten, molybdenum, rhenium and nickel. Efforts in both experimental and theoretical studies are taken into account. Aside from the potential fields of progress, the review reveals very promising performances for the emerging technologies to produce propylene, a mixture of propylene and butenes, or a liquid fuel from ethylene.

scholarly journals Study of deactivation in mesocellular foam carbon (MCF-C) catalyst used in gas-phase dehydrogenation of ethanol

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yoottapong Klinthongchai ◽  
Seeroong Prichanont ◽  
Piyasan Praserthdam ◽  
Bunjerd Jongsomjit
Keyword(s):  
Catalytic Activity ◽  
Pore Size ◽  
Gas Phase ◽  
Surface Area ◽  
Active Sites ◽  
Operating Temperature ◽  
Coke Formation ◽  
Ethanol Conversion ◽  
Deactivation Of Catalyst ◽  
Dehydrogenation Of Ethanol

AbstractMesocellular foam carbon (MCF-C) is one the captivating materials for using in gas phase dehydrogenation of ethanol. Extraordinary, enlarge pore size, high surface area, high acidity, and spherical shape with interconnected pore for high diffusion. In contrary, the occurrence of the coke is a majority causes for inhibiting the active sites on catalyst surface. Thus, this study aims to investigate the occurrence of the coke to optimize the higher catalytic activity, and also to avoid the coke formation. The MCF-C was synthesized and investigated using various techniques. MCF-C was spent in gas-phase dehydrogenation of ethanol under mild conditions. The deactivation of catalyst was investigated toward different conditions. Effects of reaction condition including different reaction temperatures of 300, 350, and 400 °C on the deactivation behaviors were determined. The results indicated that the operating temperature at 400 °C significantly retained the lowest change of ethanol conversion, which favored in the higher temperature. After running reaction, the physical properties as pore size, surface area, and pore volume of spent catalysts were decreased owing to the coke formation, which possibly blocked the pore that directly affected to the difficult diffusion of reactant and caused to be lower in catalytic activity. Furthermore, a slight decrease in either acidity or basicity was observed owing to consumption of reactant at surface of catalyst or chemical change on surface caused by coke formation. Therefore, it can remarkably choose the suitable operating temperature to avoid deactivation of catalyst, and then optimize the ethanol conversion or yield of acetaldehyde.

scholarly journals The Effect of Iron Impurities on Transition Metal Catalysts for the Oxygen Evolution Reaction in Alkaline Environment: Activity Mediators or Active Sites?

2020 ◽  
Author(s):  
Ioannis Spanos ◽  
Justus Masa ◽  
Aleksandar Zeradjanin ◽  
Robert Schlögl
Keyword(s):  
Transition Metal ◽  
Oxygen Evolution ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Water Electrolysis ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Alkaline Water Electrolysis ◽  
Co Catalysts ◽  
Model Transition

AbstractThere is an ongoing debate on elucidating the actual role of Fe impurities in alkaline water electrolysis, acting either as reactivity mediators or as co-catalysts through synergistic interaction with the main catalyst material. This perspective summarizes the most prominent oxygen evolution reaction (OER) mechanisms mostly for Ni-based oxides as model transition metal catalysts and highlights the effect of Fe incorporation on the catalyst surface in the form of impurities originating from the electrolyte or co-precipitated in the catalyst lattice, in modulating the OER reaction kinetics, mechanism and stability. Graphic Abstract

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.

scholarly journals High Pressure Photoreduction of CO2: Effect of Catalyst Formulation, Hole Scavenger Addition and Operating Conditions

Catalysts ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 430 ◽  
Author(s):  
Elnaz Bahadori ◽  
Antonio Tripodi ◽  
Alberto Villa ◽  
Carlo Pirola ◽  
Laura Prati ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Formic Acid ◽  
Gas Phase ◽  
Operating Conditions ◽  
Flame Spray ◽  
Co2 Solubility ◽  
Total Consumption ◽  
Solubility In Water ◽  
Hole Scavenger ◽  
Fuels And Chemicals

The photoreduction of CO2 is an intriguing process which allows the synthesis of fuels and chemicals. One of the limitations for CO2 photoreduction in the liquid phase is its low solubility in water. This point has been here addressed by designing a fully innovative pressurized photoreactor, allowing operation up to 20 bar and applied to improve the productivity of this very challenging process. The photoreduction of CO2 in the liquid phase was performed using commercial TiO2 (Evonink P25), TiO2 obtained by flame spray pyrolysis (FSP) and gold doped P25 (0.2 wt% Au-P25) in the presence of Na2SO3 as hole scavenger (HS). The different reaction parameters (catalyst concentration, pH and amount of HS) have been addressed. The products in liquid phase were mainly formic acid and formaldehyde. Moreover, for longer reaction time and with total consumption of HS, gas phase products formed (H2 and CO) after accumulation of significant number of organic compounds in the liquid phase, due to their consecutive photoreforming. Enhanced CO2 solubility in water was achieved by adding a base (pH = 12–14). In basic environment, CO2 formed carbonates which further reduced to formaldehyde and formic acid and consequently formed CO/CO2 + H2 in the gas phase through photoreforming. The deposition of small Au nanoparticles (3–5 nm) (NPs) onto TiO2 was found to quantitatively influence the products distribution and increase the selectivity towards gas phase products. Significant energy storage in form of different products has been achieved with respect to literature results.

scholarly journals Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species

2018 ◽  
Vol 20 (10) ◽  
pp. 7243-7253 ◽  
Author(s):  
Jesper Norell ◽  
Raphael M. Jay ◽  
Markus Hantschmann ◽  
Sebastian Eckert ◽  
Meiyuan Guo ◽  
...  
Keyword(s):  
Electronic State ◽  
Structural Dynamics ◽  
Chemical Species ◽  
Inversion Symmetry ◽  
Chemical Dynamics ◽  
Transient Species ◽  
X Ray ◽  
X Ray Scattering ◽  
Electronic Spin ◽  
Ray Scattering

Inversion-symmetry separation of electronic state manifolds in RIXS enables identification of transient species in photo-chemical dynamics.

Photocatalytic degradation of 2-propanol over TiO2-based thin films in a simulated pilot microreactor

2021 ◽  
Vol 02 ◽  
Author(s):  
Corrado Garlisi ◽  
Ahmed Yusuf ◽  
Giovanni Palmisano
Keyword(s):  
Thin Films ◽  
Gas Phase ◽  
Continuous Flow ◽  
Molecular Diffusion ◽  
Batch Reactor ◽  
High Surface ◽  
Operating Conditions ◽  
Flow Mode ◽  
Doped Tio2 ◽  
Kinetics Of

Background: Microreactor devices have attracted increasing attention over the last years due to their high surface-to-volume ratio which ensures a high heat and mass transfer, short molecular diffusion distance and greater spatial illumination homogeneity compared to traditional reactors. Objective: The aim of this study was to model the kinetics of photodegradation of 2-propanol over TiO2-based thin films in a gas-phase batch-reactor and simulate their performance in a microreactor device. Methods: The reaction was carried out in a gas-phase batch-reactor assessing the reactivity of a single-layer nitrogen (N)-doped TiO2 and a bilayer consisting of N-doped TiO2 as a bottom layer and copper (Cu)-doped TiO2 as a top layer. The kinetics of the photocatalytic process was modelled by Langmuir–Hinshelwood (LH) model. The constants obtained from LH model were used to simulate the performance of the photocatalysts in a microreactor operating in a continuous flow mode and investigating the effect of the volumetric flow rate (Q), initial concentration of pollutant (Co), number of microchannels (n) and microchannel length (l) on the photodegradation of 2-propanol. Results: N-Cu-TiO2 exhibited a higher reactivity but a lower to adsorption ability towards the target pollutant compared to N-TiO2. To maximize and leverage the advantages of microreactor, optimal operating conditions for a continuous flow mode, at steady state, should be moderately low Q and Co, long l and moderate n that minimizes flow maldistribution in parallel. Conclusion: The findings in this work could serve as a basis to design and fabricate efficient microreactors for the removal of VOC in air purification applications.

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