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

Development of stable bimetallic catalysts for carbon dioxide reforming of methane

The chemistry of methane reforming with carbon dioxide and its current and potential applications

Ni-Co bimetallic catalyst with a general formula of Ni-Co-Al-Mg-O prepared using coprecipitation has shown excellent stability and high activity for CO2 reforming of CH4 in our previous research. This paper focuses on the effects of Ni-Co content of the catalyst, attempting to avoid carbon formation on the catalyst. Catalyst samples with Ni and Co loadings ranging between 1.83 and 14.5 wt.% and 2.76 and 12.9 wt.%, respectively, were prepared and the activity and stability for CO2 reforming of CH4 was tested at 750 °C and 1 atm using a high GHSV of 180,000 mL/gcat h. The results show that catalysts with lower Ni-Co content (1.83–3.61 wt.% for Ni and 2.76–4.53 wt.% for Co) had higher and more stable activity with no deactivation and no detectable carbon formation and that those of higher Ni-Co content (5.28–14.5 wt.% for Ni and 7.95–12.9 wt.% for Co) experienced apparent deactivation with significant carbon formation in 250 h time-on-stream tests. Catalyst characterizations using TEM, XRD, H2-TPR, TG/DTG-TPO, N2-physisorption, and CO-chemisorption indicate that catalyst with lower Ni-Co content has larger surface area, smaller metal particles and better metal dispersion and therefore gives rise to better catalytic performance. The absence of large metal particles (>10 nm) is believed essential to the complete suppression of the carbon formation during reaction.

Effects of metal content on activity and stability of Ni-Co bimetallic catalysts for CO2 reforming of CH4

Ni–Al2O3 catalysts prepared by solution combustion method for syngas methanation

Investigations on the characterization of oxidic nickel phases in NiO/γ-Al 2 O 3 catalysts in a wide temperature range were carried out by means of temperature-programmed reduction (TPR), oxidation (TPO)and X-ray diffraction (XRD) methods. The results suggest a bimodal nature of oxidic nickel species that are “fixed” to the support. The differences in reducibility of catalysts calcined and reoxidized at the same temperatures were shown.

On the nature of oxidic nickel phases in NiO/γ-Al2O3 catalysts

A series of alumina supported ruthenium-nickel catalysts with varying amounts of both components have been examined by temperature-programmed reduction (TPR), oxidation (TPO) and X-ray diffraction (XRD). At a low doping content of ruthenium the promoting influence on the reduction of the oxidic nickel phase is clear but insignificant. The reduction of bimetallic catalysts occurs at much lower temperatures, as compared to a monometallic nickel catalyst, convincingly showing that ruthenium and nickel must be in close interaction with each other. However, due to the bidispersive character of the ruthenium oxide phase in calcined samples, only partial alloying of both metals takes place during the catalyst reduction. An exposure of the reduced samples to oxygen up until relatively high temperature (773 K) does not destroy the bimetallic particles. The increase of the reoxidation temperatures above 800 K leads gradually to the full segregation of nickel and ruthenium oxide species.

Characterization of alumina supported nickel-ruthenium systems

A series of alumina-supported nickel–platinum systems containing varying amounts of both components has been studied by temperature-programmed reduction (TPR) and oxidation (TPO), X-ray diffraction (XRD) and hydrogen chemisorption. The reduction of calcined catalyst precursors was enhanced by even a small amount of platinum dopant. Alloy formation was established by both TPR and XRD methods, although the linear relationship between the lattice parameters and the bimetallic composition (Vegard's law) was not followed. Chemisorption data indicate an enrichment of the surface of the catalysts in nickel.

Temperature-programmed reduction of alumina-supported Ni–Pt systems

The paper presents the results of calorimetric tests of segment elements of fireplace inserts. The aim of the work was to optimize their thermal power by replacing the previously used gray cast iron with flake graphite with gray iron with vermicular graphite and replacing the existing geometry of the heat transfer surface with a more developed one. It turned out that the thermal power of the test segments made of cast iron with vermicular graphite was higher compared to the segments of the same shape made of gray cast iron with flake graphite. It was found that the use of segments made of vermicular cast iron with a ferritic matrix allowed for an increase in the thermal power value by dozen percent, compared to segments of the same shape made of vermicular cast iron with a pearlitic matrix. The test results showed that the thermal power of the test segments depends on the variant of the development of both the heat receiving surface and the heat giving off surface. The highest value of the thermal power was obtained when ribbing in the form of a lattice was used on both of these surfaces, and the lowest when using flat surfaces.

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Influence of Microstructure and Heat Transfer Surface on the Thermal Power of Cast Iron Heat Exchangers

This paper presents an original design of a test apparatus for calorimetric measurements of arc efficiency η and melting efficiency ηm in welding processes. The construction and principle of operation of a new flow calorimeter are described, as well as the method for determining the η and ηm values in the process of the surface melting of aluminium–silicon alloy casting surfaces with a concentrated heat flux generated by the TIG (Tungsten Inert Gas) method. The results obtained indicate the advisability of using calorimetric testing to assess the arc efficiency of welding processes. It was demonstrated that changing the welding current and arc scanning speed, as well as changing the chemical composition of the silumin, has an effect on the arc efficiency value η. This has the effect of introducing a different amount of heat into the area of the heated material. The consequence of this is a change in the value of the melting efficiency ηm, which results in a change in the width and depth of the surface melting areas, through this, the cooling conditions of the material. As is well known, this will affect the microstructure of the welds and the width and microstructure of the heat-affected zone, and thus the performance of the welded joints.

https://www.mdpi.com/1996-1944/15/20/7389/pdf?version=1666676933

M. Lenik

Papers

On the nature of oxidic nickel phases in NiO/γ-Al2O3 catalysts

Characterization of alumina supported nickel-ruthenium systems

Temperature-programmed reduction of alumina-supported Ni–Pt systems

Influence of Microstructure and Heat Transfer Surface on the Thermal Power of Cast Iron Heat Exchangers

Calorimetric Method for the Testing of Thermal Coefficients of the TIG Process