Yasotha Kathiraser

Progress in Synthesis of Highly Active and Stable Nickel‐Based Catalysts for Carbon Dioxide Reforming of Methane

In recent decades, rising anthropogenic greenhouse gas emissions (mainly CO2 and CH4 ) have increased alarm due to escalating effects of global warming. The dry carbon dioxide reforming of methane (DRM) reaction is a sustainable way to utilize these notorious greenhouse gases. This paper presents a review of recent progress in the development of nickel-based catalysts for the DRM reaction. The enviable low cost and wide availability of nickel compared with noble metals is the main reason for persistent research efforts in optimizing the synthesis of nickel-based catalysts. Important catalyst features for the rational design of a coke-resistant nickel-based nanocatalyst for the DRM reaction are also discussed. In addition, several innovative developments based on salient features for the stabilization of nickel nanocatalysts through various means (which include functionalization with precursors, synthesis by plasma treatment, stabilization/confinement on mesoporous/microporous/carbon supports, and the formation of metal oxides) are highlighted. The final part of this review covers major issues and proposed improvement strategies pertaining to the rational design of nickel-based catalysts with high activity and stability for the DRM reaction.

Simultaneous Tuning Porosity and Basicity of Nickel@Nickel–Magnesium Phyllosilicate Core–Shell Catalysts for CO2 Reforming of CH4

Ni@Ni-Mgphy (Ni-Mgphy = Ni-Mg phyllosilicate) core-shell catalysts were designed by hydrothermally treating Ni@SiO2 nanoparticles with magnesium nitrate salt. The porosity and basicity of the catalysts were easily tuned by forming Ni-Mgphy shell using Ni originating from Ni@SiO2 during the hydrothermal treatment process and Mg(NO3)2 as the Ni and Mg sources, respectively. Among Ni@Ni-Mgphy core-shell catalysts synthesized under different hydrothermal durations, the catalyst treated for 10 h achieved the best catalytic performance for CO2 reforming of CH4 reaction with stable CO2 and CH4 conversions of around 81% and 78%, respectively, within 95 h reaction duration at 700 °C. The high Ni accessibility, strong basicity, and high structural stability for Ni@Ni-Mgphy core-shell catalyst with 10 h treatment time accounted for its superb catalytic performance. This method to simultaneously tune the porosity and basicity of Ni@SiO2 core-shell nanoparticles demonstrates a general way to modify the properties of other silica based core-shell nanoparticles through treating them with different metal salts.

Facile Synthesis of High Surface Area Yolk–Shell Ni@Ni Embedded SiO2 via Ni Phyllosilicate with Enhanced Performance for CO2 Reforming of CH4

Ni@Ni embedded SiO2 yolk–shell nanocomposites with controllable specific surface area are synthesized by using a facile self‐templating method via the transformation of Ni phyllosilicate (NiPhy). NiPhy is found to form initially at the interface of Ni and SiO2, stretching its branches within the whole SiO2 shell and outward onto the SiO2 surface. Upon calcination and reduction, NiPhy decomposes to smaller Ni nanoparticles within the SiO2 shell to form a Ni@Ni embedded SiO2 yolk–shell nanocomposite with high surface area, high Ni dispersion, and strong interaction between Ni and SiO2. The nanocomposite with a treatment time of 12 h exhibits stable and high CO2 and CH4 conversions of 82 and 74 %, respectively, for the CO2 reforming reaction of CH4 at 700 °C within the testing period of 50 h. This interfacial transformation method is promising for the synthesis of other Ni@NiM (M=Cu, Zn, and Mg) phyllosilicate yolk–shell nanocomposites for application as adsorbents and catalysts of other processes.

CO2 reforming of methane over highly active La-promoted Ni supported on SBA-15 catalysts: mechanism and kinetic modelling

Various Ni catalysts were synthesized by combining a high surface area SBA-15 support, a novel preparation method using an oleic acid precursor to obtain highly dispersed and small Ni particles, and the basic property of La. The activity test shows that the La-promoted Ni/SBA-15 catalyst has much higher catalytic activity and stability than unpromoted Ni/SBA-15 catalysts in the CO2 (dry) reforming of methane (DRM) reaction due to the crucial role of La to simultaneously adsorb CO2 and remove deposited carbon from the Ni metal surface. The optimization of La content shows that only a small amount of La around 1 wt% is necessary to achieve the best catalytic performance. The reaction mechanism was then proposed and kinetic modeling (for pilot scale) was performed to find the rate-determining step (RDS) in the DRM reaction for this 1% La-promoted Ni/SBA-15 catalyst. The obtained fitting result shows that CH4 decomposition is the RDS for this catalyst with an apparent activation energy of around 40.8 kJ mol−1 which is similar to the activation energies reported for common Ni-based supported catalysts.

Oxidative CO2 Reforming of Methane in La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) Hollow Fiber Membrane Reactor

CO2 utilization in catalytic membrane reactors for syngas production is an environmentally benign solution to counter the escalating global CO2 concerns. In this study, integration of a La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) hollow fiber membrane reactor with Ni/LaAlO3-Al2O3 catalyst for the oxidative CO2 reforming of methane (OCRM) reaction was successfully tested for 160 h of reaction. High CH4 and CO2 conversions of ca. 94% and 73% were obtained with O2 flux ca. 1 mL·min(-1)·cm(-2) at 725 °C for the 160-h stability test. Surface temperature programmed desorption studies of the membrane were conducted with H2, CO, and CO2 as probe gases to facilitate understanding on the effect of H2 and CO product gases as well as CO2 reactant gases on the membrane surface. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analysis of the postreacted membrane after 160-h stability tests suggests Sr-enriched phases with the presence of adsorbed carbonate and hydrogenated carbon. This shows the subsequent reactant spillover on the membrane surface from the catalyst bed took place due to the reaction occurring on the catalyst. However, XRD analysis of the bulk structure does not show any phase impurities, thus confirming the structural integrity of the LSCG hollow fiber membrane.

Ni and/or Ni–Cu alloys supported over SiO2 catalysts synthesized via phyllosilicate structures for steam reforming of biomass tar reaction

In this paper, we describe the synthesis of Ni/SiO2 and Ni–Cu/SiO2 catalysts derived from phyllosilicate structures (Ni/SiO2P and Ni–Cu/SiO2P, respectively) for steam reforming of biomass tar reaction. The steam reforming of biomass tar reaction was investigated with cellulose as a biomass model compound. The influence of steam-to-carbon ratio and reaction temperatures was also explored. Overall, the catalysts synthesized via phyllosilicate structures gave better catalytic performance than the catalysts prepared by the impregnation method. An optimum catalyst composition of 30Ni–5Cu/SiO2P gave superior catalytic performance in terms of stability and activity compared to all other catalysts. At 600 °C, about 78% of biomass was converted to gaseous products over 30Ni–5Cu/SiO2P, which is the highest among all the catalysts tested. Temperature-programmed reduction results indicate that the metal–support interaction of Ni/SiO2P catalyst prepared via phyllosilicate structures is stronger due to the unique layered structure compared to that prepared by conventional impregnation (10Ni/SiO2). The formation of a unique layered structure in Ni/SiO2P and Ni–Cu/SiO2P was also confirmed through TEM analysis. The surface elemental composition results obtained from XPS analysis show that the Cu/Ni surface molar ratio for Ni–Cu/SiO2P catalysts is consistent with the actual molar ratio values obtained from SEM-EDX analysis. This result suggests that the bimetallic catalysts synthesized via the phyllosilicate structure route can yield uniformly distributed alloy species.

Synthesis and evaluation of highly dispersed SBA-15 supported Ni–Fe bimetallic catalysts for steam reforming of biomass derived tar reaction

Highly dispersed Ni–Fe bimetallic catalysts supported on mesoporous SBA-15 were synthesized via an incipient wetness impregnation method by impregnation of a small amount of oleic acid mixed with a metal precursor on the SBA-15 support. This catalyst system was then tested for the steam reforming of biomass tar. Cellulose was used as a biomass model compound for this reaction. Among the various compositions tested, an optimum catalyst composition of 6Ni–1Fe/SBA-15 gave superior catalytic performance in terms of stability and activity. At 600 °C, about 90% of biomass was converted to gaseous products over the 6Ni–1Fe/SBA-15 catalyst, which was the highest among all the catalysts tested. From X-ray diffraction analysis, the Ni metal and Ni–Fe alloy crystallite sizes were barely distinguishable due to the formation of nano-catalysts less than 3 nm in size. Metal particles of less than 3 nm in size were further confirmed through TEM analysis. Moreover, temperature programmed reduction studies indicate a uniform distribution of bi-metallic Ni–Fe species which possess strong metal–support interactions with the mesoporous SBA-15 support. This was also indicated via X-ray photoelectron spectroscopy results. TGA studies over the spent catalysts showed that all Fe containing catalysts generally had lower carbon deposition rates compared to those over the 7Ni/SBA-15 catalyst.

CO2 as an Oxidant for High-Temperature Reactions

This paper presents a review on the developments in catalyst technology for the reactions utilizing CO2 for high temperature applications. These include dehydrogenation of alkanes to olefins, the dehydrogenation of ethylbenzene to styrene and finally CO2 reforming of hydrocarbon feedstock (i.e. methane) and alcohols. Aspects on the various reaction pathways are also highlighted. The literature on the role of promoters and catalyst development is critically evaluated. Most of the reactions discussed in this review are exploited in industries and related to on-going processes, thus providing extensive data from literature. However some reactions, such as CO2 reforming of ethanol and glycerol which have not reached industrial scale are also reviewed owing to their great potential in terms of sustainability which are essential as energy for the future. This review further illustrates the building-up of knowledge which shows the role of support and catalysts for each reaction and the underlying linkage between certain catalysts which can be adapted for the multiple CO2-related reactions.

Catalytic Biomass Gasification to Syngas Over Highly Dispersed Lanthanum-Doped Nickel on SBA-15

Catalytic biomass gasification is an environmentally benign solution to energy problems. A series of Ni catalysts on mesoporous SBA‐15 are synthesized with various La2O3 loadings. The catalytic activity of unpromoted Ni/SBA‐15 catalyst indicates that it has a high carbon formation rate, resulting in fast deactivation. In contrast, addition of La2O3 to Ni/SBA‐15 catalyst helps to remove deposited carbon by formation of oxycarbonate, resulting in higher CO production. A 1 % La doping in the Ni/SBA‐15 catalyst is sufficient to achieve high activity and stability in biomass gasification with various raw materials and in the steam reforming of toluene as a tar model compound. The combination of small metal particle size, high metal dispersion, high surface area of SBA‐15, the crucial role of La in carbon removal, and the novel synthesis method result in a highly active, stable, and effective 1 % La‐Ni/SBA‐15 catalyst for biomass gasification.