Fukui Xiao

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.

The synthesis of glycerol carbonate from glycerol and CO2 over La2O2CO3–ZnO catalysts

The transformation of CO2 and glycerol into glycerol carbonate was carried out by using acetonitrile as coupling agent over La2O2CO3–ZnO in the present work. A series of La–Zn mixed oxide catalysts with different molar ratios were prepared and calcined at different temperatures. The catalysts were characterized by N2 physisorption, XRD, XPS, FT-infrared spectroscopy and temperature-programmed desorption of CO2. The results revealed that the formation of La2O2CO3 improved the surface basicity which then favors the CO2 activation and the carbonate yield was shown to be correlated with the amount of moderately basic sites. The XPS measurement demonstrated that La2O2CO3 favored the electron transfer from zinc atoms to lanthanum atoms or oxygen atoms which then favors the activation of glycerol. The synergism between ZnO and La2O2CO3 is responsible for the high catalytic activities of the La–Zn catalysts. The best result was obtained on the catalyst with molar ratio of La:Zn = 1:4 and calcination at 500 °C.

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 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.

Synthesis of glycerol carbonate by direct carbonylation of glycerol with CO2 over solid catalysts derived from Zn/Al/La and Zn/Al/La/M (M = Li, Mg and Zr) hydrotalcites

Zn/Al/La and Zn/Al/La/M (M = Li, Mg, Zr) mixed oxides were obtained by calcination of hydrotalcite precursors and tested for glycerol carbonate (GC) synthesis from CO2 carbonylation. The results indicated the catalytic activity may be associated with the large specific surface area, the high surface content of Zn and the high binding energy of Zn atoms as well as the high density of moderately basic sites. The good result was obtained on the catalyst with a molar ratio of Zn : La : Al = 4 : 1 : 1 and, within a certain range, glycerol conversion and GC yield increase linearly upon the increase of the density of moderately basic sites. In addition, the catalytic activity was obviously improved upon introduction of Li, Mg and Zr. The effect of reaction parameters on the carbonylation of glycerol was also studied. The DRIFTS results suggest that the activated CO2 may be in the form of a bridged bidentate carbonate that inserts into zinc glycerolate to form an intermediate species of a seven-membered ring ester followed by intramolecular rearrangement to produce GC. Theoretical calculation results indicated that the seven-membered ring ester has good stability and the formation process happens spontaneously.

Carbon Dioxide Capture by MgO-modified MCM-41 Materials

MgO/MCM-41 materials with weak basic sites were synthesized by dispersing MgO onto mesoporous Si-MCM-41. Such MgO-modified MCM-41 materials were characterized by Fourier-transform infrared spectroscopy (FT-IR), temperature programmed desorption (TPD), X-ray diffraction (XRD) and N2 adsorption/desorption measurements. The results indicated that the surface area, pore size and pore volume of the materials decreased with the introduction of MgO. Their CO2 uptakes could be significantly improved when the MgO loading was increased from 0 wt% to 20 wt%. CO2-TPD and in situ FT-IR measurements showed that the materials possessed weak basic sites which could react with CO2 to form bicarbonate species and thereby improve the CO2 uptake. As a result, the adsorbed CO2 could be desorbed completely from the sample at 200 °C. In addition, the MgO/MCM-41 materials had a high thermal stability and showed promising performances in practical applications.

Recent progress in phosgene-free methods for synthesis of dimethyl carbonate

Dimethyl carbonate (DMC) is considered as an environmentally benign chemical due to negligible ecotoxicity, low bioaccumulation, and low persistence. However, the traditional process of DMC synthesis via phosgene and methanol is limited in industry owing to the toxic raw material involved. Thus, environmentally friendly phosgene-free processes for DMC production have been proposed and developed in the past decades. Until now, the alternatives appear to be the oxidative carbonylation of methanol, the transesterification of propylene or ethylene carbonate (PC or EC), the methanolysis of urea, and the direct synthesis of DMC from CO2 with methanol. In this review, we present some recent developments of these phosgene-free approaches and their prospects for industrialization.

CO2 splitting via two step thermochemical reactions over doped ceria/zirconia solid solutions

Thermochemical CO2 splitting was carried out over Ni-, Fe-, Mg- and Mn-doped ceria/zirconia solid solutions, where the sample was thermally reduced at 1400 °C under inert atmosphere followed by the re-oxidization of CO2 to generate CO at 1100 °C in the subsequent step. Compared with the undoped sample, all the doped ceria/zirconia had a high reduction yield in the first thermal reduction step. Due to the low thermal stability, Ni-, Fe- and Mn-doped samples showed lower CO production in the CO2 splitting step than the stoichiometric amounts. In contrast, the Mg-doped sample produced more CO with the volumes of 5.64 and 5.17 mL g−1 during the two thermochemical cycles. Moreover, a 10% Mg-doped sample prepared via hydrothermal treatment with P123 showed a more stable reactivity during cycling due to the relatively stable microstructure under the successive high temperature thermal treatment.

Performance of the La–Mn–Zn–Cu–O Based Perovskite Precursors for Methanol Synthesis from CO2 Hydrogenation

A series of La–Mn–Zn–Cu–O based perovskite ceramic precursors were prepared and characterized by XRD, N2-adsorption, SEM, H2-TPR, N2O-adsorption, XPS and TPD techniques. Both La2CuO4 and LaMnO3 perovskite structures were observed for the materials and more defects and the “metal-on oxide” can be realized via reduction. It was found that the samples with both La2CuO4 and LaMnO3 structures showed better catalytic performance for methanol synthesis from CO2/H2. Higher methanol selectivity might due to the appearance of Cuα+ that derived from the abundant defects of perovskite structure. The ratio of both Cuα+ and Cu0 species to the total copper species was the significant factor for the CO2 conversion.Graphical Abstract

Nitrogen-functionalized reduced graphene oxide as carbocatalysts with enhanced activity for polyaromatic hydrocarbon hydrogenation

In this study, nitrogen atoms are successfully introduced into the skeleton of reduced graphene oxide (rGO) by thermal treatment under an ammonia atmosphere. The activities of the catalysts are tested for anthracene hydrogenation, over which nearly complete anthracene conversion (99%) and high selectivity to the deeply hydrogenated products (around 50%) are achieved. The synergy of graphitic N and the sp2 CC structure can activate anthracene via π–π interactions. Moreover, the pyridinic N can facilitate hydrogen dissociative adsorption. The cooperation between anthracene activation and hydrogen dissociative adsorption results in different catalytic activities of the catalysts. Moreover, the catalysts also show better catalytic performance for the hydrogenation of other polyaromatic hydrocarbons.