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.

A review of dry (CO2) reforming of methane over noble metal catalysts

Supported Catalysts Weiting Yu,† Marc D. Porosoff,† and Jingguang G. Chen*,†,‡,§ †Catalysis Center for Energy Innovation, Department of Chemical and Bimolecular Engineering, University of Delaware, Newark, Delaware 19716, United States ‡Department of Chemical Engineering, Columbia University, New York, New York 10027, United States Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, United States

Review of Pt-based bimetallic catalysis: from model surfaces to supported catalysts.

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.

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Ni-based bimetallic heterogeneous catalysts for energy and environmental applications

Steam reforming of methane is an extremely important process for the hydrogen and syngas production. Nickel-based catalysts have been extensively employed in the industrial process of steam reforming because of their high activity, low cost, and the plentiful supply of Nickel. Nickel-based catalysts have also shown high activity for CO2 reforming of methane, which has been considered as a good option, with consumption of a significant amount of carbon dioxide. However, a major challenge is that Ni catalysts have a high thermodynamic potential for coke formation during reforming reactions. For steam reforming, coke formation induces deactivation of the catalyst, especially if the carbon forms as carbon filaments. The filamentous carbon material has a high mechanical strength and can cause mechanical deformation of the catalyst. For CO2 reforming, coke formation over Ni catalyst is even more serious and leads to rapid deactivation of the catalyst. It is highly desired to design and synthesize a coke resistant Ni catalyst not only for reforming of methane, but also for reforming of other hydrocarbons (including biomass derived hydrocarbons). Herein we summarize the very recent progresses in the design, synthesis, and characterization of coke resistant Ni catalysts for steam and CO2 reforming of methane. The progresses in the use of promoters, in the effect of supporting materials and in the preparation methods have been discussed. The thermal stability, regeneration, and future development of coke resistant Ni catalysts for these processes are also briefly addressed.

Progresses in the Preparation of Coke Resistant Ni-based Catalyst for Steam and CO2 Reforming of Methane

The CO2 (dry) reforming of methane (DRM) reaction is an environmentally benign process to convert two major greenhouse gases into synthesis gas for chemical and fuel production. A great challenge for this process involves developing catalysts with high carbon resistance abilities. Herein we synthesize, for the first time, a yolk–satellite–shell structured Ni–yolk@Ni@SiO2 nanocomposite for the DRM reaction by varying the shell thickness of Ni@SiO2 core shell nanoparticles. The formation of Ni–yolk@Ni@SiO2 is proved to be shell thickness dependent. Compared with Ni@SiO2, Ni–yolk@Ni@SiO2 with 11.2 nm silica shell thickness shows stable and near equilibrium conversion for CH4 and CO2 for 90 h at 800 °C with negligible carbon deposition. The dual effects of formation of small satellite Ni particles due to strong Ni–SiO2 interactions and yolk shell structures contribute to its high activity and stability. These findings shed light on the design of other metal yolk silica shell nanocomposites to be utilized in r...

Yolk–Satellite–Shell Structured Ni–Yolk@Ni@SiO2 Nanocomposite: Superb Catalyst toward Methane CO2 Reforming Reaction

Nanostructured Pt- and Ni-based catalysts for CO2-reforming of methane

Ni, Cu and Cu–Ni nanostructures have been fabricated and homogeneously embedded on ultrathin two-dimensional (2D) carbon nitride (g-C3N4), and the surface morphology and composition of the resulting hybrid nanostructures were studied by XRD, TEM, HRTEM-elemental mapping, Raman spectroscopy and XPS. The new hierarchical hetero-structures dropcasted on GC anodes have been visualised by SEM and their catalytic performance have been examined in methanol electrooxidation reaction (MOR) under alkaline conditions. Nanosized Ni particles dispersed finely over g-C3N4 are very active electrocatalysts with MOR onset at potential 0.35 V and charge transfer resistance 0.12 kΩ. The stability of modyfied GC electrodes, examined under chronoamperometric conditions showed that for electrode loading with 4% (wt. %) of NiO the stable current density ca. 36 A g−1 (12 A cm2) was obtained during whole experiment (up to 160 min). For all catalyst studied the curent density obtained during MOR reaction was enhanced when electrode was iluminated by UV light λ∼400 nm, and the highest value were obtained for 4% Ni/CN catalyst ca. 127 A g−1 (22 A cm2). The Cu incorporation in the hybrid material evoke loss of activity mostly due to Cu+ irreversible reduction/oxidation to Cu° and Cu2+, CuO segregation and influencing electron transfer process which results in the increasing in the redox potential. These results represent an important step towards light-enhanced electro-reactive systems and sensors in which heterojunction formation can facilitate electron-hole separation and enable more efficient energy transfer.

Electrocatalytic methanol oxidation over Cu, Ni and bimetallic Cu-Ni nanoparticles supported on graphitic carbon nitride

Nanostructured PtNi catalysts, prepared by the reverse microemulsion method (ME) and supported on a nanofibrous alumina were studied for the CO2-reforming of methane. Monometallic (Ni and Pt) and bimetallic (PtNi) supported catalysts were synthesized, characterized (XRD, TEM, Elemental Analysis, Raman, XPS and temperature-programmed reduction (TPR)) and tested under CO2-reforming reaction conditions. Catalysts prepared by wetness impregnation (IM) of the support were also synthesized for comparative purposes. Characterization results showed that Pt addition and the preparation of the catalysts by ME promoted the formation of NiO, instead of NiAl2O4, and facilitated its reduction to Ni0 during the catalysts pre-treatment. It was also observed that the Ni and Pt ensembles were modified when the catalysts were prepared by the reverse microemulsion method, reducing the global carbon formation. From activity tests it can be concluded that catalysts prepared by the reverse microemulsion method are less sensitive to coke deposition and more stable under CO2-reforming conditions. Besides, in the bimetallic catalysts, there is a Pt-Ni interaction between metallic centers, which enhances the catalyst stability and selectivity towards H2 and CO.

Izabela S. Pieta

Papers

Nanostructured Pt- and Ni-based catalysts for CO2-reforming of methane

Electrocatalytic methanol oxidation over Cu, Ni and bimetallic Cu-Ni nanoparticles supported on graphitic carbon nitride

Improved Pt-Ni nanocatalysts for dry reforming of methane

In situ DRIFT–TRM study of simultaneous NOx and soot removal over Pt–Ba and Pt–K NSR catalysts

Transient study of the dry reforming of methane over Pt supported on different γ-Al2O3