This review will explore the influences of the active metal, support, promoter, preparation methods, calcination temperature, reducing environment, particle size and reactor choice on catalytic activity and carbon deposition for the dry reforming of methane Bimetallic (Ni−Pt, Ni−Rh, Ni−Ce, Ni−Mo, Ni−Co) and monometallic (Ni) catalysts are preferred for dry reforming compared to noble metals (Rh, Ru and Pt) due to their low-cost Investigation of support materials indicated that ceria−zirconia mixtures, ZrO2 with alkali metals (Mg2+, Ca2+, Y2+) addition, MgO, SBA-15, ZSM-5, CeO2, BaTiO3 and Ca08Sr02TiO3 showed improved catalytic activities and decreased carbon deposition The modifying effects of cerium (Ce), magnesium (Mg) and yttrium (Y) were significant for dry reforming of methane MgO, CeO2 and La2O3 promoters for metal catalysts supported on mesoporous materials had the highest catalyst stability among all the other promoters Preparation methods played an important role in the synthesis of smaller particle size and higher dispersion of active metals Calcination temperature and treatment duration imparted significant changes to the morphology of catalysts as evident by XRD, TPR and XPS Catalyst reduction in different environments (H2, He, H2/He, O2/He, H2−N2 and CH4/O2) indicated that probably the mixture of reducing agents will lead to enhanced catalytic activities Smaller particle size (

Dry reforming of methane: Influence of process parameters—A review

A short review of catalysis for CO2 conversion

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.

Catalyst design for dry reforming of methane: Analysis review

Carbon nanotubes are promising materials for various applications. In recent years, progress in manufacturing and functionalizing carbon nanotubes has been made to achieve the control of bulk and surface properties including the wettability, acid–base properties, adsorption, electric conductivity and capacitance. In order to gain the optimal benefit of carbon nanotubes, comprehensive understanding on manufacturing and functionalizing carbon nanotubes ought to be systematically developed. This review summarizes methodologies of manufacturing carbon nanotubes via arc discharge, laser ablation and chemical vapor deposition and functionalizing carbon nanotubes through surface oxidation and activation, doping of heteroatoms, halogenation, sulfonation, grafting, polymer coating, noncovalent functionalization and nanoparticle attachment. The characterization techniques detecting the bulk nature and surface properties as well as the effects of various functionalization approaches on modifying the surface properties for specific applications in catalysis including heterogeneous catalysis, photocatalysis, photoelectrocatalysis and electrocatalysis are highlighted.

Carbon nanotube catalysts: recent advances in synthesis, characterization and applications.

CO2 reforming of CH4 was carried out over Ni–alumina aerogel catalysts prepared with various Ni loadings. The preparation of alumina supported Ni catalysts via sol–gel synthesis and subsequent supercritical drying led to the formation of very small metal particles, which are evenly distributed over the alumina support. The activity of the aerogel catalysts increased along with increasing metal loading, and eventually, the SAA25 (0.25 in Ni/Al mole ratio) catalyst exhibited the high activity comparable to that of a 5 wt.% Ru/alumina catalyst (ESCAT44, Engelhard). Compared to the alumina-supported Ni catalyst prepared by conventional impregnation method, Ni–alumina aerogel catalysts showed a remarkably low coking rate due to highly dispersed metal particles. From TEM micrograph studies, it was observed that the formation of filamentous carbon was significantly influenced by the metal particle size and proceeded mostly over the metal particles larger than 7 nm. The loss of catalytic activity at 973 K was mainly caused by coke deposition and sintering.

Effect of metal particle size on coking during CO2 reforming of CH4 over Ni–alumina aerogel catalysts

A fast sol−gel synthetic route for obtaining alumina aerogels has been developed by modifying the tranditional method under appropriately controlled conditions. The highly mesoporous alumina aerogel prepared by our new sol−gel synthesis method and CO2 supercritical drying had a surface area in excess of 700 m2/g and high thermal stability.

Fast sol-gel synthetic route to high-surface-area alumina aerogels

Mesoporous nickel–alumina aerogel catalysts with high surface area have been prepared by CO2 supercritical drying of alcogels obtained by the fast sol–gel process. The nickel phase was uniformly distributed in the alumina gel network from transparent monolithic nickel–alumina co-gels by using nickel acetate as a metal precursor. The nickel–alumina aerogel catalysts prepared were characterized by nitrogen adsorption–desorption, TG/DTA, and reaction test, and their properties were compared with those of conventionally impregnated catalysts. Alumina aerogel-based nickel catalysts exhibited good activity and marked stability against coking in methane dry reforming.

Nickel–alumina aerogel catalysts prepared by fast sol–gel synthesis

The low viscosity of the TiO 2 –MnO–SiO 2 based ternary welding flux system has been studied using the rotating spindle method to understand the influence of TiO 2 /SiO 2 and MnO on the viscous behavior at high temperatures. Viscosity slightly decreased with increased TiO 2 /SiO 2 and MnO due to the limited absolute amount of SiO 2 content and also the depolymerization of the flux due to the supply of free oxygen (O 2 − ) from the basic oxides of MnO and TiO 2 . The flux structure, which directly affects the viscosity of the flux, was verified by using Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). FTIR results showed that the transmittance trough depth of the NBO/Si tetrahedral structure became less pronounced with higher MnO and TiO 2 due to the relative decrease in the absolute SiO 2 concentration and dominant of higher basicity. The Si O Ti bending vibration trough also showed a marked decrease with the additions of MnO and TiO 2 , which suggests that the change in viscosity for the present flux system may also be the depolymerization of the bridged oxygen in the Si O Ti complex network structures. XPS analysis suggested a slight decrease in the O° and an increase in the O 2 − , O − with higher TiO 2 and MnO. Thus, a decrease in the viscosity of the flux with higher TiO 2 /SiO 2 and MnO content correlated well with the FTIR and XPS analyses. The apparent activation energy for viscous flow was found to be between 40 and 105 kJ/mol.

Influence of TiO2/SiO2 and MnO on the viscosity and structure in the TiO2–MnO–SiO2 welding flux system

The effect of TiO 2 /SiO 2 and SiO 2 /Al 2 O 3 ratio on the wettability of the TiO 2 –MnO–SiO 2 –Al 2 O 3 quaternary welding flux system was studied using the sessile drop method by measuring the contact angle at the liquid/solid interface. The contact angle was measured at 1773 K to determine the relationship between wettability and flux structure, which is affected by the flux composition. The surface and interfacial tensions of the TiO–MnO–SiO 2 –Al 2 O 3 flux system were calculated using Boni's equation and Young's equation, respectively, based on the measured contact angle. The adhesion energy, which corresponds to the energy required to separate the flux from a substrate, was calculated using Dupre's equation. The interfacial tension between the liquid flux and Pt-10Rh decreased and the surface tension increased with higher TiO 2 and Al 2 O 3 . The results of the Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses of as-quenched fluxes from 1773 K also support the structural relationship with the wettability. It was found that both O − ( non-bridged oxygen ) and O 2  − ( free oxygen ) affect the interfacial tension between the flux and the substrate.

Jin-Hong Kim

Papers

Effect of metal particle size on coking during CO2 reforming of CH4 over Ni–alumina aerogel catalysts

Fast sol-gel synthetic route to high-surface-area alumina aerogels

Nickel–alumina aerogel catalysts prepared by fast sol–gel synthesis

Influence of TiO2/SiO2 and MnO on the viscosity and structure in the TiO2–MnO–SiO2 welding flux system

High-temperature wettability and structure of the TiO2–MnO–SiO2–Al2O3 welding flux system