Nannan Sun

Effect of pore structure on Ni catalyst for CO2 reforming of CH4

Ni–CaO–ZrO2 catalysts with different pore structures were prepared and tested for CO2 reforming of methane. It was found that the catalyst with a mesoporous framework showed both high activity and stability. In particular, no deactivation was observed at a period of run on stream. The characterization confirmed that the “confine effect” of the mesoporous structure prevented Ni particles from sintering during reaction, and as a result, the catalyst with such a mesoporous framework showed a better catalytic performance and resistance to coking.

Preparation and activity of Cu/Zn/Al/Zr catalysts via hydrotalcite-containing precursors for methanol synthesis from CO2 hydrogenation

A series of Cu/Zn/Al/Zr catalysts were synthesized by calcination of hydrotalcite-containing precursors with different Cu2+/Zn2+ atomic ratios (n). Two other catalysts (n = 2) were also prepared via phase-pure hydrotalcite-like and conventional rosasite precursors for comparison. XRD and UV-Vis-NIR DRS characterizations demonstrate that most Cu2+ of hydrotalcite-containing materials did not enter the layer structure. The Cu dispersion of the catalysts decreases with the increase of Cu content, while both the exposed Cu surface area and the Cu+ and Cu0 content on the reduced surface reach a maximum when n is 2. The catalytic performance for the methanol synthesis from CO2 hydrogenation was also tested. The catalytic activity and selectivity of the catalysts (n = 0.5–4) via hydrotalcite-containing precursors rise first and then decrease with increasing Cu2+/Zn2+ ratios, and the optimum performance is obtained over the catalyst with Cu2+/Zn2+ = 2. Moreover, the Cu/Zn/Al/Zr catalyst (n = 2) via hydrotalcite-containing precursor exhibits the best catalytic performance, which is mainly due to the maximum content of active species compared with another two catalysts derived from different precursors.

Grafting of Amines on Ethanol-Extracted SBA-15 for CO2 Adsorption

SBA-15 prepared via ethanol extraction for template removing was grafted with three kinds of amine precursors (mono-, di-, tri-aminosilanes) to synthesis new CO2 adsorbents. The SBA-15 support and the obtained adsorbents were characterized by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), N2 adsorption/desorption, thermogravimetry (TG), elemental analysis, Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that, except higher silanol density, the ethanol-extracted SBA-15 support possessed a more regular mesophase and thicker walls than traditionally calcined samples, leading to a good stability of the adsorbent under steam treatment. The adsorption capacity of different amine-grafted samples was found to be influenced by not only the surface amine density, but also their physiochemical properties. These observations provide important support for further studies of applying amine-grafted adsorbents in practical CO2 capture process.

The Properties of Individual Carbon Residuals and Their Influence on The Deactivation of Ni–CaO–ZrO2 Catalysts in CH4 Dry Reforming

Ni–CaO–ZrO2 catalysts with different properties were prepared and tested for CO2 reforming of methane. The catalysts were characterized by means of transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction to reveal their distinct properties and carbon deposition behaviors in the reforming reaction. It was found that the catalyst prepared by a coprecipitation method and ageing by heating to reflux exhibited a nanocrystalline structure with strong metal–support interaction, which was responsible for both high activity and stability, but it also exhibited the highest carbon formation rate among the tested catalysts. This result suggests that catalyst deactivation might not necessarily correlate with the amount of formed carbon, and the individual properties of carbon residuals could play a more decisive role. Carbon residuals on different catalysts were identified as amorphous carbon, encapsulating carbon, whisker carbon, and graphite, which had different influence on the deactivation. On the surface of the most active and stable catalyst, the carbon species mainly consisted of amorphous and whisker carbon, suggesting that the formation of such carbon species does not necessarily lead to catalyst deactivation. In contrast, the deactivation was found to be closely related to the formation of encapsulating carbon and graphite, which could coat the catalyst surface. The accumulation of different carbon residuals was proven to follow a formation–diffusion/elimination scenario, which was significantly influenced by the Ni particle size and Ni–ZrO2 interactions.

The bi-functional mechanism of CH4 dry reforming over a Ni–CaO–ZrO2 catalyst: further evidence via the identification of the active sites and kinetic studies

A mesoporous Ni–CaO–ZrO2 catalyst which showed an excellent performance in the dry reforming of CH4 was thoroughly characterized by using a series of methods including N2 physical adsorption, temperature-programmed reduction (TPR), H2/CO chemisorptions, and so forth. Particularly, samples after different treatments such as calcination, reduction and different periods of reaction were subjected to X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis, by which changes in the phase structure and surface chemistry were followed. The results suggested that metallic Ni was gradually oxidized during the reaction, and a non-stoichiometric Ni–carbon compound was slowly formed. This latter species has a role as an important intermediate (or even active phase). Kinetic studies were then carried out based on these findings, according to which a Langmuir–Hinshelwood model was developed. Both the experimental results and the kinetic analysis provided novel evidence for the bi-functional mechanism of dry reforming over ZrO2-based catalysts.

Highly stable mesoporous NiO–Y2O3–Al2O3 catalysts for CO2 reforming of methane: effect of Ni embedding and Y2O3 promotion

A series of mesoporous NiO–Y2O3–Al2O3 composite oxides with different yttrium contents were synthesized by either a one-pot evaporation-induced self-assembly (EISA) method or impregnation for carbon dioxide reforming of methane (CRM). Their catalytic performance was evaluated and all the samples were characterized by means of N2 physisorption, XRD, XPS, H2-TPR and TEM. It was found that addition of appropriate amounts of Y2O3 (sample NYA2) has little influence on the EISA process, and thus, an ordered mesoporous structure with enhanced textural and Ni dispersive properties can be obtained. The NYA2 catalyst showed excellent performance in CRM, and no deactivation was observed for 100 h. Based on the comparative characterization of the reduced and exhausted catalysts, the good performance of NYA2 was related to its low carbon formation rate thanks to the very small and thermally stable metallic Ni particles (ca. 6.0 nm) which were well embedded in the catalyst framework and the redox properties of the Y2O3 promoter.

Solid Adsorbents for Low-Temperature CO2 Capture with Low-Energy Penalties Leading to More Effective Integrated Solutions for Power Generation and Industrial Processes

CO2 capture represents the key technology for CO2 reduction within the framework of CO2 capture, utilization, and storage (CCUS). In fact, the implementation of CO2 capture extends far beyond CCUS since it will link the CO2 emission and recycling sectors, and when renewables are used to provide necessary energy input, CO2 capture would enable a profitable zero- or even negative-emitting and integrated energy-chemical solution. To this end, highly efficient CO2 capture technologies are needed, and adsorption using solid adsorbents has the potential to be one of the ideal options. Currently, the greatest challenge in this area is the development of adsorbents with high performance that balances a range of optimization-needed factors, those including costs, efficiency, and engineering feasibility. In this review, recent advances on the development of carbon-based and immobilized organic amines-based CO2 adsorbents are summarized, the selection of these particular categories of materials is because they are among the most developed low temperature (<100 oC) CO2 adsorbents up to date, which showed important potential for practical deployment at pilot-scale in the near future. Preparation protocols, adsorption behaviors as well as pros and cons of each type of the adsorbents are presented, it was concluded that encouraging results have been achieved already, however, the development of more effective adsorbents for CO2 capture remains challenging and further innovations in the design and synthesis of adsorbents are needed.

Facile one-pot synthesis of mesoporous carbon and N-doped carbon for CO2 capture by a novel melting-assisted solvent-free method

A facile and efficient one-pot melting-assisted solvent-free method was successfully developed for the first time to produce hierarchically mesoporous carbon and nitrogen-enriched mesoporous carbon materials. This method used a very simple thermal treatment process instead of normally reported solvent-based preparations, thus making it potentially very applicable for fast and large scale production of mesoporous carbons. The obtained carbon materials were comprehensively characterized by X-ray diffraction, Raman spectroscopy, N2 sorption, scanning electron microscopy, transmission electron microscopy, CHN analysis, X-ray photoelectron spectroscopy, and elemental mapping. The results show that the as-synthesized carbon materials possess well-developed hierarchical porous structures, uniform pore sizes, and high surface areas, and the specific structures can be adjusted by changing the temperature and duration of the thermal treatment process. Moreover, the resultant carbon material with a high surface area of 748 m2 g−1 exhibits excellent CO2 capture properties with a capacity of 2.73 mmol g−1 at 298 K and 1 bar, and a CO2 selectivity of 21.6 under flue gas conditions. More importantly, due to the successful incorporation of large amounts of highly dispersed N in the carbon matrix (11.67%), the as-synthesized NMC sample exhibits a significantly enhanced CO2 capacity of 1.66 mmol g−1 with an excellent CO2 selectivity of 240.7 at 348 K and 1 bar, revealing great promise for practical CO2 capture applications.

Surface-modified spherical activated carbon materials for pre-combustion carbon dioxide capture

Surface modification of activated carbon beads via HNO3 oxidation and subsequent amination at elevated temperatures was investigated as a means to improve their performance for CO2 capture, and the effects of the resultant changes in porosity and surface chemistry on adsorption characteristics of the samples were studied. Characterisations conducted with elemental analysis, physical adsorption, X-ray photoelectron spectroscopy and scanning electron microscope demonstrate that both the porosity and surface chemistry of the carbon beads were tuned by the modification without any alteration of the integrity of the desirable spherical morphology. Adsorption evaluation with both thermogravimetric analysis and high pressure volumetric analysis under various conditions indicate that one of the modified samples had a high CO2 adsorption capacity (8.64 mmol g−1 at 20 bar and 30 °C) with fast adsorption/desorption kinetics, superior durability and good selectivity over N2 and H2. Both the unique spherical form (diameter = 1.2 ± 0.2 mm) and the superior adsorption performance render the modified carbon beads a promising candidate for CO2 capture especially in pre-combustion capture using pressure swing adsorption.

Effect of pore geometries on the catalytic properties of NiO–Al2O3 catalysts in CO2 reforming of methane

Mesoporous NiO–Al2O3 catalysts were prepared by an evaporation-induced self-assembly (EISA) method, during which the amount of HNO3 added in the precursor solution was varied. Characterization results indicated that the phase structure, component interaction and surface chemistry are fairly similar for all the samples, while the dispersion and textural properties, which are determined by the structure of the micelles and reaction rate of hydrolysis during the EISA process, changed significantly, thus leading to considerably different catalytic performance in CO2 reforming of methane (CRM). The well-known trend that carbon formation rate decreases with the decrease of Ni particle size was observed in the current NA-Hx samples, however, it is very interesting that the disordered slit-like pores endowed the NA-H32 sample with a better capability to inhibit carbon formation as it showed substantially fewer carbon deposits as compared with NA-H16 (ordered cylindrical pore), despite the fact that the Ni particles in these samples are of similar size. In summary, the excellent performance of the NA-H32 catalyst in comparison to other non-promoted NiO–Al2O3 catalysts holds promise for using this cost-effective system in practical CRM applications.