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Devendra Pakhare

Bio: Devendra Pakhare is an academic researcher from Louisiana State University. The author has contributed to research in topics: Carbon dioxide reforming & Catalysis. The author has an hindex of 9, co-authored 9 publications receiving 1485 citations.

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Journal ArticleDOI
TL;DR: Dry (CO2) reforming of methane literature for catalysts based on Rh, Ru, Pt, and Pd metals is reviewed, including the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.
Abstract: Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.

1,472 citations

Journal ArticleDOI
TL;DR: In this paper, the active sites and kinetics of dry reforming of methane (DRM) on lanthanum zirconate (LZ) pyrochlore catalysts are studied as a function of Rh substitution, temperature and partial pressures of CH4 and CO2.

140 citations

Journal ArticleDOI
TL;DR: In this paper, three catalysts were tested: La2Zr2O7 [LZ] and two pyrochlores in which Zr in the B-site has been isomorphically partially substituted with (a) Ru (2.00 ǫ) and (b) Pt (3.78 ) in an on-stream time of 600 min.
Abstract: Dry (CO2) reforming of methane (DRM) is a highly endothermic reaction (ΔH = +59.1 kcal/mol) producing syngas (H2 and CO) with the H2/CO ratio of ~1. DRM requires reaction temperatures above ~800 °C for complete equilibrium conversion to CO and H2, and is inevitably accompanied by carbon deposition. Here we examine lanthanum zirconate (La2Zr2O7) pyrochlores, with the larger trivalent cation La and a smaller tetravalent cation Zr occupying A and B sites, respectively. Three catalysts are tested: La2Zr2O7 [LZ] and two pyrochlores in which Zr in the B-site has been isomorphically partially substituted with (a) Ru (2.00 wt%) [LRuZ] and (b) Pt (3.78 wt%) [LPtZ]. The levels of substitution by weight correspond to identical atomic levels of substitution at the B-site. Here, activation energies are determined as a function of Ru or Pt substitution on the B-site. The results show that activation energies based on both CH4 and CO2 reaction rates are much lower for LRuZ than LPtZ. Conversion of CH4 ( X CH 4 ) and CO2 ( X CO 2 ) was greater for LRuZ compared to LPtZ at 525 °C, 575 °C, and 625 °C throughout an on-stream time of 600 min. After each 600-min run, temperature programmed oxidation (TPO) showed that total carbon formation decreased with increasing reaction temperature, although the stability of the deposited carbon increased with increasing reaction temperature.

86 citations

Journal ArticleDOI
TL;DR: In this article, steady-state isotopic transient kinetic analysis (SSITKA) was used to elucidate the migration of carbon atoms to product species in dry reforming of methane.
Abstract: Increases in worldwide methane production from biological and fossil sources have led to an increased level of interest in the dry reforming of methane (DRM) to produce syngas. Experimental efforts have shown that select pyrochlore materials, such as the Rh-substituted lanthanum zirconate pyrochlore (LRhZ), are catalytically active for DRM, exhibit long-term thermal stability, and resist deactivation. This work seeks to allow further catalyst improvements by elucidating surface reaction kinetics via steady-state isotopic transient kinetic analysis (SSITKA) of dry reforming on the LRhZ pyrochlore. Isotopically labeled CH4 and CO2 were used in multiple SSITKA experiments to elucidate the migration of carbon atoms to product species. Short surface residence times at 650 and 800 °C (<0.6 s) were observed for DRM intermediates involved in reversible reactions, and the participation of all surface metal atoms as active sites for DRM, not only Rh, is suggested. Isotopic responses and kinetic isotope effects are ...

55 citations

Journal ArticleDOI
TL;DR: In this article, a 1% Ru-substituted lanthanum strontium zirconate pyrochlore, La1.97Sr0.03Ru0.05Zr1.95O7 (LSRuZ), was compared to a commercially available 0.5% Ru/Al2O3 catalyst at different bed temperatures and reactant feed ratios.
Abstract: Dry reforming of methane (DRM) was performed on a 1% Ru-substituted lanthanum strontium zirconate pyrochlore, La1.97Sr0.03Ru0.05Zr1.95O7 (LSRuZ), and results were compared to a commercially available 0.5% Ru/Al2O3 catalyst at different bed temperatures and reactant feed ratios. X-ray diffraction of the fresh LSRuZ confirmed the formation of the La2Zr2O7 pyrochlore face-centered crystal lattice using a modified Pechini synthesis procedure. Results from X-ray photoelectron spectroscopy (XPS) on the fresh calcined pyrochlore showed the presence of RuO2, which was also present along with both RuO3 and RuO4 in the 0.5% Ru/Al2O3 catalyst. Temperature-programmed reduction (TPR) showed that Ru was reducible in both catalysts, but the primary TPR peak for Ru reduction was 140 °C higher for the LSRuZ pyrochlore than that for 0.5% Ru/Al2O3, consistent with the incorporation of Ru within the pyrochlore. The effect of the CH4/CO2 feed ratio on the activity was studied by varying the feed ratio as 1:1, 2:1, and 1:2 at ...

52 citations


Cited by
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Journal ArticleDOI
TL;DR: Dry (CO2) reforming of methane literature for catalysts based on Rh, Ru, Pt, and Pd metals is reviewed, including the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.
Abstract: Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.

1,472 citations

Journal ArticleDOI
TL;DR: The current state-of-the-art and a critical assessment of plasma-based CO2 conversion, as well as the future challenges for its practical implementation are presented.
Abstract: CO2 conversion into value-added chemicals and fuels is considered as one of the great challenges of the 21st century. Due to the limitations of the traditional thermal approaches, several novel technologies are being developed. One promising approach in this field, which has received little attention to date, is plasma technology. Its advantages include mild operating conditions, easy upscaling, and gas activation by energetic electrons instead of heat. This allows thermodynamically difficult reactions, such as CO2 splitting and the dry reformation of methane, to occur with reasonable energy cost. In this review, after exploring the traditional thermal approaches, we have provided a brief overview of the fierce competition between various novel approaches in a quest to find the most effective and efficient CO2 conversion technology. This is needed to critically assess whether plasma technology can be successful in an already crowded arena. The following questions need to be answered in this regard: are there key advantages to using plasma technology over other novel approaches, and if so, what is the flip side to the use of this technology? Can plasma technology be successful on its own, or can synergies be achieved by combining it with other technologies? To answer these specific questions and to evaluate the potentials and limitations of plasma technology in general, this review presents the current state-of-the-art and a critical assessment of plasma-based CO2 conversion, as well as the future challenges for its practical implementation.

667 citations

Journal ArticleDOI
TL;DR: In this review, recent research advances in electrocatalytic CO2 reduction are summarized from both experimental and theoretical aspects and are expected to provide new insights into the further technique development and practical applications of CO2 electroreduction.
Abstract: The worldwide unrestrained emission of carbon dioxide (CO2) has caused serious environmental pollution and climate change issues. For the sustainable development of human civilization, it is very desirable to convert CO2 to renewable fuels through clean and economical chemical processes. Recently, electrocatalytic CO2 conversion is regarded as a prospective pathway for the recycling of carbon resource and the generation of sustainable fuels. In this review, recent research advances in electrocatalytic CO2 reduction are summarized from both experimental and theoretical aspects. The referred electrocatalysts are divided into different classes, including metal–organic complexes, metals, metal alloys, inorganic metal compounds and carbon-based metal-free nanomaterials. Moreover, the selective formation processes of different reductive products, such as formic acid/formate (HCOOH/HCOO−), monoxide carbon (CO), formaldehyde (HCHO), methane (CH4), ethylene (C2H4), methanol (CH3OH), ethanol (CH3CH2OH), etc. are introduced in detail, respectively. Owing to the limited energy efficiency, unmanageable selectivity, low stability, and indeterminate mechanisms of electrocatalytic CO2 reduction, there are still many tough challenges need to be addressed. In view of this, the current research trends to overcome these obstacles in CO2 electroreduction field are summarized. We expect that this review will provide new insights into the further technique development and practical applications of CO2 electroreduction.

613 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the effect of metal support and metal support-promoter combinations on the performance and stability of bi-and tri-metallic catalysts for dry reforming of methane, and concluded that a catalyst design must take into account not only the separate effects of the active metal, support and promoter, but also include the combined and mutual interactions of these components.
Abstract: The performance of catalysts used for the dry reforming of methane can strongly depend on the selection of active metals, supports and promoters. This work studies their effects on the activity and stability of selected catalysts. Designing an economically viable catalyst that maintains high catalytic activity and stability can be achieved by exploiting the synergic effects of combining noble and/or non-noble metals to form highly active and stable bi- and tri-metallic catalysts. Perovskite type catalysts can also constitute a potent and cost effective substituent. Metal oxide supports with surface Lewis base sites are able to reduce carbon formation and yield a greater stability to the catalyst, while noble metal promoters have proven to increase both catalyst activity and stability. Moreover, a successful metal-support-promoter combination should lead to higher metal-support interacrtion, lower reduction temperature and enhancement of the anti-coking and anti-amalgamation properties of the catalyst. However, the effect of each parameter on the overall performance of the catalyst is usually complex, and the catalyst designer is often faced with a tradeoff between activity, stability and ease of activation. Based on the review carried out on various studies, it is concluded that a catalyst design must take into consideration not only the separate effects of the active metal, support and promoter, but should also include the combined and mutual interactions of these components.

556 citations

Journal ArticleDOI
TL;DR: A detailed overview of the development of nickel-based bimetallic catalysts for energy and environmental applications is provided in this article, where a detailed account is provided on the utilization of these systems in the catalytic reactions related to energy production and environmental remediation.
Abstract: Bimetallic catalysts have attracted extensive attention for a wide range of applications in energy production and environmental remediation due to their tunable chemical/physical properties. These properties are mainly governed by a number of parameters such as compositions of the bimetallic systems, their preparation method, and their morphostructure. In this regard, numerous efforts have been made to develop “designer” bimetallic catalysts with specific nanostructures and surface properties as a result of recent advances in the area of materials chemistry. The present review highlights a detailed overview of the development of nickel-based bimetallic catalysts for energy and environmental applications. Starting from a materials science perspective in order to obtain controlled morphologies and surface properties, with a focus on the fundamental understanding of these bimetallic systems to make a correlation with their catalytic behaviors, a detailed account is provided on the utilization of these systems in the catalytic reactions related to energy production and environmental remediation. We include the entire library of nickel-based bimetallic catalysts for both chemical and electrochemical processes such as catalytic reforming, dehydrogenation, hydrogenation, electrocatalysis and many other reactions.

525 citations