From thermal catalysis to plasma catalysis: a review of surface processes and their characterizations
Abstract: The use of atmospheric pressure plasma to enhance catalytic chemical reactions involves complex surface processes induced by the interactions of plasma-generated fluxes with catalyst surfaces. Industrial implementation of plasma catalysis necessitates optimizing the design and realization of plasma catalytic reactors that enable chemical reactions that are superior to conventional thermal catalysis approaches. This requires the fundamental understanding of essential plasma-surface interaction mechanisms of plasma catalysis from the aspect of experimental investigation and theoretical analysis or computational modeling. In addition, experimental results are essential to validate the relative theoretical models and hypotheses of plasma catalysis that was rarely understood so far, compared to conventional thermal catalysis. This overview focuses on two important application areas, nitrogen fixation and methane reforming, and presents a comparison of important aspects of the state of knowledge of these applications when performed using either plasma-catalysis or conventional thermal catalysis. We discuss the potential advantage of plasma catalysis over thermal catalysis from the aspects of plasma induced synergistic effect and in situ catalyst regeneration. In-situ/operando surface characterization of catalysts in plasma catalytic reactors is a significant challenge since the high pressure of realistic plasma catalysis systems preclude the application of many standard surface characterization techniques that operate in a low-pressure environment. We present a review of the status of experimental approaches to probe gas-surface interaction mechanisms of plasma catalysis, including an appraisal of demonstrated approaches for integrating surface diagnostic tools into plasma catalytic reactors. Surface characterizations of catalysts in plasma catalytic reactors demand thorough instrumentations of choices of plasma sources, catalyst forms, and the relative characterization tools. We conclude this review by presenting open questions on self-organized patterns in plasma catalysis.
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Topics: Catalysis (51%)
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7 results found
Open access•Journal Article•
Abstract: A New Scanning Tunneling Microscope Reactor Used for High Pressure and High Temperature Catalysis Studies Feng Tao †‡ , David Tang †‡ , Miquel Salmeron † , and Gabor A. Somorjai †‡ * Materials Science Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720 † Department of Chemistry, University of California, Berkeley, CA 94720 ‡ Abstract We present the design and performance of a homebuilt high pressure and high temperature reactor equipped with a scanning tunneling microscope for catalytic studies. In this design, the STM body, sample and tip are placed in a small high pressure reactor (~19 cm -3 ) located within an ultrahigh vacuum (UHV) chamber. A sealable port on the wall of the reactor separates the high pressure environment of reactant gases from the vacuum environment of the STM chamber, and permits the exchange of sample and tip in UHV. A combination of a sample transfer arm, wobble stick, and sample load-lock system allows transfer of samples and tips between the preparation chamber, high pressure reactor and ambient environment. Experiments performed on three samples both in vacuum and in high pressure conditions demonstrate the capability of in-situ investigations of heterogeneous catalysis and surface chemistry at atomic resolution at a wide pressure range from UHV to a pressure higher than one atmosphere and a temperature range from 300 K to 700 K. * To whom correspondence should be addressed.
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Topics: Scanning tunneling microscope (52%)
2 Citations
Abstract: Non-thermal plasma (NTP) coupled with catalysis provides a way to enable the dry reforming of methane (DRM) reaction to occur at low temperatures. While assistance of NTP brings the negative issue of coke deposition due to the faster rate of CH4 dissociation induced by NTP. Herein, β-Mo2C was employed as an effective component to activate CO2 and collaborated with Ni/γ-Al2O3 for the plasma-assisted DRM reaction. Addition of β-Mo2C facilitated the charge deposition, and Ni nanoparticles were found to re-disperse over the β-Mo2C surface due to the strong interaction between Ni and β-Mo2C. Benefiting from the new active interface of Ni-Mo2C, the mechanically mixed Mo2C-Ni/Al2O3 catalyst exhibited much better activity and stability as compared with the undoped Ni/Al2O3 catalyst. The present study reveals the crucial roles of β-Mo2C additives, providing practical solutions to depress carbon deposition, and thereby enhance the catalytic stability in plasma-assisted DRM reaction.
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Topics: Carbon dioxide reforming (56%), Catalysis (53%)
1 Citations
Abstract: The rate, selectivity and efficiency of plasma-based conversion processes is strongly affected by nonequilibrium phenomena. High concentrations of vibrationally excited molecules are such a plasma-induced effect. It is frequently assumed that vibrationally excited molecules are important in plasma catalysis because their presence lowers the apparent activation energy of dissociative chemisorption reactions and thus increases the conversion rate. A detailed atomic-level understanding of vibrationally stimulated catalytic reactions in the context of plasma catalysis is however lacking. Here, we couple a recently developed statistical model of a plasma-induced vibrational nonequilibrium to molecular dynamics simulations, enhanced sampling methods, and machine learning techniques. We quantify the impact of a vibrational nonequilibrium on the dissociative chemisorption barrier of H2 and CH4 on nickel catalysts over a wide range of vibrational temperatures. We investigate the effect of surface structure and compare the role of different vibrational modes of methane in the dissociation process. For low vibrational temperatures, very high vibrational efficacies are found, and energy in bend vibrations appears to dominate the dissociation of methane. The relative impact of vibrational nonequilibrium is much higher on terrace sites than on surface steps. We then show how our simulations can help to interpret recent experimental results, and suggest new paths to a better understanding of plasma catalysis.
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Topics: Dissociation (psychology) (54%)
1 Citations
Open access•
Matthias Filez1, Hilde Poelman1, Ranjith Karuparambil Ramachandran1, Jolien Dendooven1 +4 more•Institutions (1)
01 Jan 2013-
Abstract: X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF) were combined in situ to study the ALD-based synthesis of Pt catalysts. This first time combination of synchrotron-based techniques was applied during the (methylcyclopentadienyl)trimethylplatinum/ozone deposition process executed at 150 °C on a silica support. A nucleation delay indicative for nanoparticle formation was observed for Pt loadings below 1 equivalent monolayer. XAS and XRF were recorded simultaneously at different catalyst loadings in this nucleation regime. Analysis of the combined in situ data yielded a quantitative picture of the evolution of the diameter, shape, lattice packing and density of the deposited Pt clusters. Additionally, the degree of oxidation at the cluster surface after the ozone pulse could be monitored. At the early start of the deposition process, Pt adatoms cluster together to form stable nuclei. A strong increase in the density of nuclei is seen below 0.16 equivalent monolayers, after which coalescence gradually occurs. From 0.04 to 0.71 equivalent monolayers, Pt clusters are fcc packed and correspond best to a hemispherical (1 1 1)-truncated cuboctahedral shape. By crosslinking the XRF and XAS data, a linear increase in cluster diameter with Pt loading is observed within this range. The surface of the Pt clusters is shown to be oxidized immediately after the ozone exposure. The degree of surface oxidation remains approximately constant for clusters with a 1–3 nm diameter. This surface oxygen is shown to be crucial for further growth during deposition. The combined application of in situ XRF and XAS thus allowed for an advanced identification of the ALD-deposited Pt nanoparticles.
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Topics: Nucleation (54%), X-ray absorption spectroscopy (52%)
1 Citations
Topics: Nanosecond (54%), Carbon dioxide reforming (52%)
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348 results found
10 Jul 1997-
Abstract: Preparation of Solid Catalysts. Characterization of Solid Catalysts. Model Systems. Elementary Steps and Mechanisms. Kinetics and Transport Processes. Deactivation and Regeneration. Special Catalytic Systems. Laboratory Reactors. Reaction Engineering. Environmental Catalysis. Inorganic Reactions. Energy-related Catalysis. Organic Reactions.
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Topics: Homogeneous catalysis (70%), Heterogeneous catalysis (63%), Organic reaction (59%) ... read more
4,157 Citations
Open access•Book•
01 Jan 2002-
Abstract: VOLUME 1: THEORY AND INSTRUMENTATION Introduction to the Theory and Practice of Vibrational Spectroscopy Instrumentation for Mid- and Far-infrared Spectroscopy Instrumentation for Near-infrared Spectroscopy Instrumentation for Raman Spectroscopy Time-resolved Spectroscopy Dichroism and Optical Activity in Vibrational Spectroscopy Surface-enhanced Vibrational Spectroscopy Other Instrumental Approaches for Vibrational Spectroscopy Calibration Procedures and Standards for Vibrational Spectroscopy VOLUME 2: SAMPLING TECHNIQUES Mid- and Near-infrared Transmission Spectroscopy Mid-infrared External Reflection Spectroscopy Mid-infrared Internal Reflection Spectroscopy Diffuse Reflection Spectroscopy Other IR Sampling Techniques Raman Spectroscopy Low Temperature and High Pressure Sampling Techniques Microscopy Depth profiling by Vibrational Spectroscopy Optical Conduits for Vibrational Specroscopy Hyphenated Techniques Atmospheric VOLUME 3: SAMPLE CHARACTERIZATION AND SPECTRAL DATA PROCESSING Spectra-Structure Correlations Group Theoretical and Numerical Approaches to the Calculation of Vibrational Spectra Discrimant Analysis Two-dimensional (2D) Analysis Spectral Enhancement and Band Resolution Techniques Quantitative Analysis Anomalies, Atifacts and Common Errors in Using Vibrational Spectroscopy Techniques Glossary VOLUME 4: APPLICATIONS IN INDUSTRY, MATERIALS AND THE PHYSICAL SCIENCES Analysis and Characterization of Polymers and Rubbers Rheo-optical Measurements of Polymers and Rubbers Materials Science Spectoelectrochemistry Process Vibrational Spectroscopy Atmospheric and Astronomical Vibrational Spectroscopy Industrial Applications of Vibrational Spectroscopy Forensic Applications of Vibrational Spectroscopy Catalysis Other Applications of Vibrational Spectroscopy Vibrational Spectroscopy in Education VOLUME 5: APPLICATIONS IN LIFE, PHARMACEUTICAL AND NATURAL SCIENCES Biomedical Applications Biochemical Applications Pharmaceutical Applications Food Science Agricultural Applications Abbreviations and Acronyms, Glossary, List of Contributors and Subject Index
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Topics: Spectroscopy (62%), Instrumental chemistry (62%), Two-dimensional infrared spectroscopy (61%) ... read more
1,996 Citations
Open access•Book•
01 Jan 2007-
Abstract: Foreword. Preface. Acknowledgments. 1 Introduction to Spectroscopic Ellipsometry. 1.1 Features of Spectroscopic Ellipsometry. 1.2 Applications of Spectroscopic Ellipsometry. 1.3 Data Analysis. 1.4 History of Development. 1.5 Future Prospects. References. 2 Principles of Optics. 2.1 Propagation of Light. 2.2 Dielectrics. 2.3 Reflection and Transmission of Light. 2.4 Optical Interference. References. 3 Polarization of Light. 3.1 Representation of Polarized Light. 3.2 Optical Elements. 3.3 Jones Matrix. 3.4 Stokes Parameters. References. 4 Principles of Spectroscopic Ellipsometry. 4.1 Principles of Ellipsometry Measurement. 4.2 Ellipsometry Measurement. 4.3 Instrumentation for Ellipsometry. 4.4 Precision and Error of Measurement. References. 5 Data Analysis. 5.1 Interpretation of (PSI, DELTA). 5.2 Dielectric Function Models. 5.3 Effective Medium Approximation. 5.4 Optical Models. 5.5 Data Analysis Procedure. References. 6 Ellipsometry of Anisotropic Materials. 6.1 Reflection and Transmission of Light by Anisotropic Materials. 6.2 Fresnel Equations for Anisotropic Materials. 6.3 4x4 Matrix Method. 6.4 Interpretation of (PSI, DELTA) for Anisotropic Materials. 6.5 Measurement and Data Analysis of Anisotropic Materials. References. 7 Data Analysis Examples. 7.1 Insulators. 7.2 Semiconductors. 7.3 Metals/Semiconductors. 7.4 Organic Materials/Biomaterials. 7.5 Anisotropic Materials. References. 8 Real-Time Monitoring by Spectroscopic Ellipsometry. 8.1 Data Analysis in Real-Time Monitoring. 8.2 Observation of Thin-Film Growth by Real-Time Monitoring. 8.3 Process Control by Real-Time Monitoring. References. Appendices. 1 Trigonometric Functions. 2 Definitions of Optical Constants. 3 Maxwell's Equations for Conductors. 4 Jones-Mueller Matrix Conversion. 5 Kramers-Kronig Relations. Index.
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Topics: Ellipsometry (59%)
1,673 Citations
Abstract: Heterogeneous catalysis is of paramount importance in chemistry and energy applications. Catalysts that couple light energy into chemical reactions in a directed, orbital-specific manner would greatly reduce the energy input requirements of chemical transformations, revolutionizing catalysis-driven chemistry. Here we report the room temperature dissociation of H2 on gold nanoparticles using visible light. Surface plasmons excited in the Au nanoparticle decay into hot electrons with energies between the vacuum level and the work function of the metal. In this transient state, hot electrons can transfer into a Feshbach resonance of an H2 molecule adsorbed on the Au nanoparticle surface, triggering dissociation. We probe this process by detecting the formation of HD molecules from the dissociations of H2 and D2 and investigate the effect of Au nanoparticle size and wavelength of incident light on the rate of HD formation. This work opens a new pathway for controlling chemical reactions on metallic catalysts.
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Topics: Plasmon (53%), Surface plasmon (52%), Feshbach resonance (52%) ... read more
1,081 Citations
Abstract: Nature Communications 4: Article number: 1828 (2013); Published: 7 May 2013; Updated: 11 February 2014. In this Article, the museum catalogue numbers for the paratype and referred specimens of Acrotholus audeti nov. gen. et. sp. were inadvertently exchanged. The paratype reference should have been ROM 2964 and the catalogue number for the referred specimen should have been ROM 2962.
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Topics: Paratype (59%)
987 Citations