Shiqiang Zhang

Bio: Shiqiang Zhang is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Catalysis & Partial oxidation. The author has an hindex of 3, co-authored 3 publications receiving 21 citations.

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.

Infrared studies of gas phase and surface processes of the enhancement of catalytic methane decomposition by low temperature plasma

Abstract: Catalyst enhancement by atmospheric pressure plasma is a recently emerging field of research that embodies a complex system of reactive species and how they interact with surfaces. In this work we use an atmospheric pressure plasma jet integrated with a nickel on Al2O3/SiO2 support catalyst material to decompose methane gas by partial oxidation reaction. We use Fourier-transform Infrared spectroscopy analysis of the gas phase post reaction to measure the loss of methane and the production of CO, CO2, and H2O and diffuse reflectance Fourier-transform Infrared spectroscopy (DRIFTs) in situ analysis of the catalyst surface as a function of both catalyst temperature and plasma operating parameters. We find reduction of methane by both plasma alone, catalyst alone, and an increase when both plasma and catalyst were simultaneously used. The production of CO appears to be due primarily to the plasma source as it only appears above 2.5 W plasma dissipated power and decreases as catalyst temperature increases. CO2 production is enhanced by having the catalyst at high temperature and H2O production depends on both plasma power and temperature. Using DRIFTs we find that both heating and plasma treatment remove absorbed water on the surface of the catalyst. Plasma treatment alone however leads to the formation of CO and another IR spectral feature at 1590 cm−1, which may be attributed to carboxylate groups, bonded to the catalyst surface. These species exhibit a regime of plasma treatment where they are formed on the surface and where they are significantly removed from the catalyst surface. We see the formation of a new spectral feature at 995 cm−1 and discuss the behavior and possible origins of this feature. This research highlights the potential for plasma regeneration of catalyst materials as well as showing enhancement of the catalytic behavior under low temperature plasma treatment.

Mechanistic aspects of plasma-enhanced catalytic methane decomposition by time-resolved operando diffuse reflectance infrared Fourier transform spectroscopy

Abstract: To study mechanistic aspects of plasma-enhanced catalysis, methane is decomposed by a supported Ni catalyst assisted by an Ar/O2 atmospheric pressure plasma jet (APPJ). The time-resolved surface response of the Ni catalyst is investigated by operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) using various experimental settings. Catalyst temperatures of room temperature and 500 °C and nozzle-catalyst surface distances of 3, 5 and 8 mm were examined, and the amount of O2 of the Ar/O2 gas mixture flowing through the APPJ was either 0 or 0.5%. A synergistic effect of surface bonded C–O was observed during the exposure of the Ni catalyst to the APPJ for low oxygen operating conditions (pure Ar jet). Surface bonded C–O formed only when there was plasma present and the C–O signal was enhanced for higher catalyst temperature. When the supported Ni catalyst was subjected to the plasma-generated particle fluxes using highly oxidizing conditions, the presence of surface bonded C–O was suppressed. The plasma-catalytic CO and CO2 production in the gas phase measured downstream mirrored the surface behavior of C–O bonds when the plasma source operating condition was changed from a low oxygen portion to a high oxygen portion at high catalyst temperature (500 °C). CH n (n = 1, 2, 3) species on the catalyst surface were also studied by DRIFTS, and CH n destruction was found to correlate with C–O formation. In particular, the time-resolved CH n response showed a possible conversion process of CH n to C–O when the Ni catalyst was exposed to the plasma source. This finding may indicate a plasma-mediated regeneration of the catalyst by plasma-catalyst surface interactions.

Plasma-assisted dry reforming of methane over Mo2C-Ni/Al2O3 catalysts: Effects of β-Mo2C promoter

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.

Plasma-Catalytic Partial Oxidation of Methane on Pt(111): A Microkinetic Study on the Role of Different Plasma Species

Abstract: We use microkinetic modeling to examine the potential of plasma-catalytic partial oxidation (POX) of CH4 as a promising new approach to produce oxygenates We study how different plasma species aff

Plasma-chemical promotion of catalysis for CH4 dry reforming: unveiling plasma-enabled reaction mechanisms.

Abstract: A kinetic study revealed that a Ni/Al2O3 catalyst exhibited a drastic increase in CH4 and CO2 conversion under nonthermal plasma when lanthanum was added to the Ni/Al2O3 catalyst as a promoter. For a better fundamental understanding of the plasma and catalyst interfacial phenomena, we employed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under plasma-on conditions to elucidate the nonthermal plasma-enabled reaction enhancement mechanisms. Compared with thermal catalysis, plasma-activated CO2 shows a 1.7-fold enhancement for bidentate (1560 and 1290 cm−1) and monodentate carbonate (1425 and 1345 cm−1) formation on La. Moreover, new peaks of bicarbonate (1655 cm−1) and bridge carbonate (1720 cm−1) were formed due to nonthermal plasma interactions. CO2-TPD study after thermal- and plasma-activated CO2 treatment further confirmed that plasma-activated CO2 enhances bidentate and monodentate carbonate generation with a 1.5-fold promotion at high temperature (500 °C). XRD and EDS analyses suggest that atomic-scale interaction between CO2–La and CHx–Ni is possible over the complex La–Ni–Al oxide; vibrationally excited CO2-induced carbonates provide the key to enhancing the overall performance of CH4 dry reforming at low temperature.

Foundations of plasma catalysis for environmental applications

Abstract: Plasma catalysis is gaining increasing interest for various applications, but the underlying mechanisms are still far from understood. Hence, more fundamental research is needed to understand these mechanisms. This can be obtained by both modelling and experiments. This foundations paper describes the fundamental insights in plasma catalysis, as well as efforts to gain more insights by modelling and experiments. Furthermore, it discusses the state-of-the-art of the major plasma catalysis applications, as well as successes and challenges of technology transfer of these applications.

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.