In-situ/operando techniques to identify active sites for thermochemical conversion of CO2 over heterogeneous catalysts

2021 ◽  
Author(s):  
Kai Feng ◽  
Yaning Wang ◽  
Man Guo ◽  
Jingpeng Zhang ◽  
Zhengwen Li ◽  
...  
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Thermochemical Conversion

scholarly journals Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mengyao Ouyang ◽  
Konstantinos G. Papanikolaou ◽  
Alexey Boubnov ◽  
Adam S. Hoffman ◽  
Georgios Giannakakis ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Theoretical Calculations ◽  
Atomic Scale ◽  
Single Atom ◽  
In Situ Control ◽  
Single Atom Alloy

AbstractThe atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

In Situ Characterization of Dynamic Changes in the Microstructure and Chemistry of Catalysts

2001 ◽  
Vol 7 (S2) ◽  
pp. 1058-1059
Author(s):  
P.A. Crozier
Keyword(s):  
Electron Microscopy ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalytic Reactions ◽  
In Situ Characterization ◽  
Dynamic Changes ◽  
In Situ Electron Microscopy ◽  
Reactive Gas

Controlled atmosphere electron microscopy (CAEM) is a form of in situ microscopy in which the sample is exposed to a reactive gas during observation. This instrument essentially combines the nano-structural characterization features of a TEM with a microreactor and is ideal for studying gas/solid reactions in catalysts. Such in situ techniques can provide a link between surface studies performed under UHV conditions and catalytic reactions run in high-pressure reactors. with correctly designed experiments, CAEM is a powerful technique for correlating dynamic changes in microstructure with catalysis and can be used to provide insights on the location of active sites and mechanisms for catalysis. Baker and colleagues have worked for over thirty years on different heterogeneous catalysts using in situ electron microscopy (see [1] for example). Gai has also published many studies on the application of CAEM to oxide catalysts [2].The technique usually relies on detecting a change in the heterogeneous catalyst during a catalytic reaction.

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

scholarly journals Electrokinetic and in situ spectroscopic investigations of CO electrochemical reduction on copper

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jing Li ◽  
Xiaoxia Chang ◽  
Haochen Zhang ◽  
Arnav S. Malkani ◽  
Mu-jeng Cheng ◽  
...  
Keyword(s):  
Mass Transport ◽  
Active Sites ◽  
Gas Diffusion ◽  
Reduction Reaction ◽  
Adsorbed Hydrogen ◽  
Diffusion Type ◽  
Proton Coupled Electron Transfer ◽  
Alkaline Electrolytes ◽  
Reaction Orders

AbstractRigorous electrokinetic results are key to understanding the reaction mechanisms in the electrochemical CO reduction reaction (CORR), however, most reported results are compromised by the CO mass transport limitation. In this work, we determined mass transport-free CORR kinetics by employing a gas-diffusion type electrode and identified dependence of catalyst surface speciation on the electrolyte pH using in-situ surface enhanced vibrational spectroscopies. Based on the measured Tafel slopes and reaction orders, we demonstrate that the formation rates of C2+ products are most likely limited by the dimerization of CO adsorbate. CH4 production is limited by the CO hydrogenation step via a proton coupled electron transfer and a chemical hydrogenation step of CO by adsorbed hydrogen atom in weakly (7 < pH < 11) and strongly (pH > 11) alkaline electrolytes, respectively. Further, CH4 and C2+ products are likely formed on distinct types of active sites.

scholarly journals Morphology Controlled Synthesis of γ-Al2O3 Nano-Crystallites in Al@Al2O3 Core–Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 310
Author(s):  
Dohyeon Han ◽  
Doohwan Lee
Keyword(s):  
Electrostatic Interactions ◽  
Heterogeneous Catalysts ◽  
Metal Substrate ◽  
Inorganic Anions ◽  
Core Shell ◽  
Hydroxyl Groups ◽  
Hydrothermal Reactions ◽  
Fine Control ◽  
Reaction Processes

Fine control of morphology and exposed crystal facets of porous γ-Al2O3 is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al2O3 core–shell architecture consisting of an Al metal core and a porous γ-Al2O3 shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl−, NO3−, and SO42−), and acid–base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl−, NO3−, SO42−) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al2O3 core–shell architecture with controlled morphology and exposed crystal-facets of the γ-Al2O3 shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al2O3 nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods.

In situ construction of phenanthroline-based cationic radical porous hybrid polymers for metal-free heterogeneous catalysis

2021 ◽  
Vol 9 (12) ◽  
pp. 7556-7565
Author(s):  
Guojian Chen ◽  
Yadong Zhang ◽  
Ke Liu ◽  
Xiaoqing Liu ◽  
Lei Wu ◽  
...  
Keyword(s):  
Heterogeneous Catalysis ◽  
Heterogeneous Catalysts ◽  
Hybrid Polymers ◽  
Metal Free ◽  
Oxidation Of Sulfides

Constructing phenanthroline-based cationic radical porous hybrid polymers as versatile metal-free heterogeneous catalysts for both oxidation of sulfides and CO2 conversion.

scholarly journals Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

2021 ◽  
Author(s):  
Ricci Underhill ◽  
Mark Douthwaite ◽  
Richard J. Lewis ◽  
Peter J. Miedziak ◽  
Robert D. Armstrong ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Active Oxygen Species ◽  
Catalytic Performance ◽  
Resonance Spectroscopy ◽  
Oxygen Species ◽  
Paramagnetic Resonance ◽  
Temperature Oxidation

AbstractLow temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

Simple flow through reaction cells for in situ transmission and fluorescence x-ray-absorption spectroscopy of heterogeneous catalysts

2006 ◽  
Vol 77 (2) ◽  
pp. 023105 ◽  
Author(s):  
Simon R. Bare ◽  
George E. Mickelson ◽  
Frank S. Modica ◽  
Andrzej Z. Ringwelski ◽  
N. Yang
Keyword(s):  
Absorption Spectroscopy ◽  
Heterogeneous Catalysts ◽  
X Ray ◽  
Flow Through ◽  
X Ray Absorption ◽  
Simple Flow

Diffuse Reflectance FT-IR Characterization of Active Sites under Reaction Conditions: The Production of Oxygenates in the CO/H2 Reaction

1994 ◽  
Vol 48 (10) ◽  
pp. 1208-1212 ◽  
Author(s):  
J. J. Benítez ◽  
I. Carrizosa ◽  
J. A. Odriozola
Keyword(s):  
Infrared Spectra ◽  
Active Sites ◽  
Diffuse Reflectance ◽  
Reaction Conditions ◽  
In Situ Drifts ◽  
Ft Ir

The reactivity of a Lu2O3-promoted Rh/Al2O3 catalyst in the CO/H2 reaction is reported. Methane, heavier hydrocarbons, methanol, and ethanol are obtained. In situ DRIFTS has been employed to record the infrared spectra under the actual reaction conditions. The structure of the observed COads DRIFTS bands has been resolved into its components. The production of oxygenates (methanol and ethanol) has been correlated with the results of the deconvolution calculation. Specific sites for the production of methanol and ethanol in the CO/H2 reaction over a Rh,Lu2O3/Al2O3 catalyst are proposed.

A facile approach to fabricate halloysite/metal nanocomposites with preformed and in situ synthesized metal nanoparticles: a comparative study of their enhanced catalytic activity

2015 ◽  
Vol 44 (19) ◽  
pp. 8906-8916 ◽  
Author(s):  
Sankar Das ◽  
Subhra Jana
Keyword(s):  
Catalytic Activity ◽  
Comparative Study ◽  
Metal Nanoparticles ◽  
Heterogeneous Catalysts ◽  
Cost Effective ◽  
Environmentally Benign ◽  
Metal Nanocomposites

Halloysite/metal nanocomposites have been synthesized through the immobilization of preformed and in situ synthesized metal nanoparticles over halloysite surfaces, which in turn produce efficient, cost-effective, and environmentally benign heterogeneous catalysts.

Sign in / Sign up

Export Citation Format

Share Document