Atomic layer deposition (ALD) was applied to deposit Pt into KL zeolite channels. The location of Pt deposition and the interaction between Pt and the KL zeolite have been investigated by various characterization methods as well as DFT simulations. It has been demonstrated that Pt nanoparticles (NPs) with precisely controlled size (∼0.8 nm) and high dispersion have been successfully deposited into the micropores of the KL zeolite. The produced Pt/KL catalysts exhibited highly efficient performance for n-heptane reforming to aromatics with a high toluene selectivity up to 67.3% (toluene/total aromatics = 97.8%) and a low methane selectivity (0.9%), in spite of an ultralow Pt loading (0.21 wt%). It was revealed that the strong interaction between Pt and the KL zeolite resulting in the electron-enriched state of Pt and the confinement of Pt in the micropores of the KL zeolite facilitated the aromatization of n-heptane. The small size and high dispersion of Pt NPs contributed to inhibition of the hydrogenolysis reaction. Prevention of agglomeration of Pt NPs due to confinement inside the micropores of the KL zeolite and the strong interaction led to the high stability of the Pt/KL catalysts.

Atomic layer deposition (ALD) was applied to deposit Pt into KL zeolite channels. The location of Pt deposition and the interaction between Pt and the KL zeolite have been investigated by various characterization methods as well as DFT simulations. It has been demonstrated that Pt nanoparticles (NPs) with precisely controlled size (∼0.8 nm) and high dispersion have been successfully deposited into the micropores of the KL zeolite. The produced Pt/KL catalysts exhibited highly efficient performance for n-heptane reforming to aromatics with a high toluene selectivity up to 67.3% (toluene/total aromatics = 97.8%) and a low methane selectivity (0.9%), in spite of an ultralow Pt loading (0.21 wt%). It was revealed that the strong interaction between Pt and the KL zeolite resulting in the electron-enriched state of Pt and the confinement of Pt in the micropores of the KL zeolite facilitated the aromatization of n-heptane. The small size and high dispersion of Pt NPs contributed to inhibition of the hydrogenolysis reaction. Prevention of agglomeration of Pt NPs due to confinement inside the micropores of the KL zeolite and the strong interaction led to the high stability of the Pt/KL catalysts.

Efficient recovery of coal liquids from direct coal liquefaction residue (DCLR) is beneficial for improving the economics of the direct coal liquefaction process. An attempt was made to evaluate the possibility of extracting coal liquids from DCLR using subcritical water (SBCW). The properties of water are compared with those of typical organic solvents. With regard to the ability of dissolving/emulsifying organic components, SBCW compares favorably with some typical organic solvents under certain conditions. This is evidenced by the fact that the SBCW3 (320 °C/11.7 MPa) extraction yield is similar to the n-hexane extraction yield, although the SBCW1 (250 °C/5.2 MPa) and SBCW2 (300 °C/8.9–11.6 MPa) extraction yields are lower than the n-hexane extraction yields under comparable conditions. The recovery rate of coal liquids from DCLR by SBCW3 extraction can be higher than the maximum recovery rate by n-hexane or methanol extraction when the (SBCW3/DCLR)mass is high enough. In comparison with n-hexane-extractable, SBCW-extractable contains more high-molecular-weight and heteroatom-containing components. The group composition balances of several SBCW extractions reveal that SBCW-extractable is mainly from the n-hexane-extractable fraction of the parent DCLR, with a small amount of components from the asphaltene-type materials. The solvent utilization index decreases with the increase of extraction yield, indicating that the overall solubility/emulsibility of coal liquids in SBCW3 decreases as the extraction proceeds. This implies that more and more high-molecular-weight and low-solubility/emulsibility components are extracted from DCLR with the increase of extraction yield. Similar phenomena are found when n-hexane and methanol are used as the extraction solvents. It is also found that the SBCW3 extraction yield can be higher than the 320 °C-pyrolysis extraction yield when the (SBCW3/DCLR)mass is high enough.

Different crystallographically oriented TiO2 nanotube arrays (NTAs) were successfully fabricated via the anodization of Ti film sputtered on indium tin oxide (ITO) glass. The results indicate that the preferred orientation of TiO2 NTAs with a texture degree f > 0.9 for anatase (004) can be assembled over a wide range of water content in the electrolyte from 1.5 to 6.0 vol%. When the water content is more than 8 vol%, the anatase TiO2 NTA further transforms to a polycrystal type. When compared to the characteristics of DSSCs based on the different oriented TiO2 NTAs, the (004) preferred orientation of TiO2 NTAs possesses the highest power conversion efficiency (PCE) and electron transport rate owing to its excellent orientation.

•The addition of TiO2 strengthened Co-support interaction and caused low cobalt reduction degree.•A small amount of ZO2 suppressed the blockage of cobalt by TiOx and increased reducibility of cobalt species.•Proper reduction degree and dispersion of cobalt species at high Zr loading caused high activity.•The addition of ZrO2 improved the H2 adsorption but decreased the CO adsorption.•The addition of ZrO2 shifted the FTS product distribution to light hydrocarbons.A series of Co-based catalysts containing 10 wt.% cobalt for Fischer–Tropsch synthesis (FTS) reaction were prepared by impregnation method, in which cobalt species were supported on mesoporous silica (abbreviated as MS) doped with TiO2, ZrO2 and TiO2–ZrO2 oxides as promoters. The incorporation of promoters was observed to have a profound impact on the physic-chemical and catalytic properties of catalysts. It was shown that the dispersion of cobalt species could be improved by the addition of TiO2, resulting in higher catalytic activity on Co/TiO2–MS catalyst (abbreviated as Co/Ti–MS). Meanwhile, the reducibility of cobalt species in Co/Ti–MS was apparently inhabited due to the strong Co–TiO2 interaction, while this effect was suppressed upon a small addition of ZrO2. With the further addition of ZrO2, the reducibility and dispersion of cobalt species were increased simultaneously, resulting in the improved activity. In addition, the H2 chemisorption was enhanced while CO adsorption was suppressed by the incorporation of ZrO2, which increased the H/C ratios on the surface of Co-based catalysts, and promoted the hydrogenation of surface carbon species. Consequently, methane selectivity was enhanced and heavy hydrocarbons selectivity was suppressed in FTS product distribution. The incorporation of promoters into Co/MS catalysts also improved the electron density of cobalt species due to the electron transfer from support to Co via the MOSi structure (M = Ti or Zr). The electron enrichment of cobalt species on Co/Ti–MS catalyst caused lower H/C ratio, resulting in higher selectivity to heavy hydrocarbons and lower selectivity to methane.

Transformation behavior of carbonaceous species over a precipitated iron-based Fischer–Tropsch synthesis (FTS) catalyst was investigated by Mössbauer effect spectroscopy (MES), X-ray photoelectron spectroscopy (XPS), CO temperature-programmed desorption (CO-TPD), temperature-programmed hydrogenation (TPH), high resolution transmission electron microscopy (HRTEM) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalytic activities were tested in a fixed bed reactor. It was found that during carburization the fresh catalyst was firstly reduced from α-Fe2O3 to Fe3O4, accompanied simultaneously with the formation of atomic (Cα) and polymeric (Cβ) carbonaceous species on the surface of the catalyst. With time on stream the Fe3O4 formed in the near-surface regions was converted gradually to χ-Fe5C2, and the amounts of Cα and Cβ species presented an increasing trend. Subsequently, these species were combined partly together to form the graphitic-type (Cδ) carbonaceous species, and the Cδ species largely covered on the surface of iron carbides. The formation of iron carbides (especially for χ-Fe5C2), Cα and Cβ species on the surface layers promoted the catalytic activity, whereas the Cδ species formed restrained the active sites for FTS reaction.Graphical abstractA systematic investigation was carried on transformation mechanism of surface/bulk structures and carbonaceous species under CO atmosphere over a precipitated Fe-based catalyst, and correlation between iron phases, surface carbon species and FTS activity.Highlights► The Cα and Cβ species were formed gradually with the conversion of magnetite to χ-Fe5C2 on the surface layers under CO atmosphere. ► The formation of χ-Fe5C2, Cα and Cβ species on the surface layers promoted the catalytic activity. ► The Cδ species formed restrained the active sites for FTS reaction.

Mechanisms and kinetics for the reduction of a precipitated iron-based Fischer–Tropsch catalyst in H2 have been investigated using in situ Mössbauer effect spectroscopy (MES) and thermogravimetric (TG) method in the temperature range of 250–350 °C. In situ MES results indicate that the reduction of paramagnetic (PM) α-Fe2O3 (70%) and superparamagnetic (spm) Fe3+ (30%) in the fresh catalyst proceed via different steps. PM α-Fe2O3 is firstly reduced to magnetite and then to metallic iron, while the reduction of spm Fe3+ proceeds in three consecutive steps: it is first reduced to magnetite with a significantly rapid rate, then to non-stoichiometric wüstite, and finally to metallic iron. The reduction of PM α-Fe2O3 to Fe3O4 can be described by a two-dimensional Avrami–Erofe’ ev phase change model (formation and growth of nuclei). However, the corresponding overall reduction, which includes the reduction of PM α-Fe2O3 and spm Fe3+ to Fe3O4, can be described by a three-dimensional phase-boundary-controlled reaction model based on the overall extraction ratio of oxygen. The difference between the two models selected for the PM α-Fe2O3 reduction and the corresponding overall reduction is attributed to the rapid reduction of spm Fe3+ to Fe3O4. For the reduction of PM magnetite to α-Fe and its corresponding overall reduction (including the reduction of PM and spm Fe3O4 to α-Fe), it is found that both of them follow the Avrami–Erofe’ ev phase change model (two-dimensional or three-dimensional). The value of apparent activation energy for the overall reduction has been calculated and compared with the literature data.The reduction of iron FT catalyst in the temperature range of 250–350 °C was separated into two processes for the mathematical modeling. The overall reduction of α-Fe2O3 (PM and spm phases) to Fe3O4 can be described by a three-dimensional phase-boundary-controlled reaction model, while the overall reduction of Fe3O4 to α-Fe follows the formation and growth of nuclei model (two-dimensional or three-dimensional).

Detailed phase transformation in syngas (H2/CO = 1.2) on a precipitated iron-based catalyst was studied by N2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (LRS). Fischer–Tropsch synthesis (FTS) performance of the catalyst was investigated in a slurry-phase continuously stirred tank reactor (STSR). The hematite in the fresh catalyst was reduced initially to magnetite, and then the magnetite in the bulk reached steady state slowly with increasing reduction time. Simultaneously, the Fe3O4 on the surface layers converted gradually to iron carbides, accompanied with the continual increase in the amounts of surface carbonaceous species. In the FTS reaction, the catalytic activity presented an increased trend with gradual carburization of the catalyst by keeping the stability in the bulk Fe3O4, suggesting that the conversion of magnetite to iron carbides in the near-surface regions provides probably the active sites for FTS. In addition, the chain growth reaction was restrained and the hydrogenation reaction was enhanced with increasing reduction duration.Detailed phase transformation in syngas (H2/CO = 1.2) and Fischer–Tropsch synthesis performances of a precipitated iron-based catalyst were studied in a slurry-phase continuously stirred tank reactor. The hematite reduced firstly to magnetite with increasing reduction time, and then the bulk Fe3O4 reached gradually a steady state, accompanied with the slow conversion of the surface magnetite to iron carbides.

The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 temperature-programmed reduction (TPR), and Mössbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of α-Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of α-Fe2O3 to Fe3O4, stabilized the FeO phase, and (or) decreased the carburization degree of the catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins (C=2–4), but it had little effect on the selectivities to heavy (C5+) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.

The monodisperse SiO2 microspheres with average diameter of 230 nm made by optimized Stöber method were used as core to prepare core-shell structure SiO2@Fe2O3 catalysts with different shell thickness through hydrolysis precipitation. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 physical adsorption and X-ray diffraction (XRD) were used to characterize the size, structure and morphology of catalysts and the effects of different preparation conditions on morphology were discussed. The characterization results indicate that SiO2@Fe2O3 catalysts possess obvious core-shell structure and the spherical morphology of catalyst is kept. Iron oxide nanoparticles are attached to the silica surface through hydroxyl-bond and a 2–10 nm thick dense shell is formed.

Three hydrocracking catalysts were prepared by impregnation method with different incorporation manners of Ni/W metals on HY/Al2O3 support. The effect of combination methods on acidity, hydrogenation capability of the catalysts and its hydrocracking performance on FT wax was studied. The balance between hydrogenation performance and cracking performance could be modulated by adjusting the metal-support combination methods. Ni/W pre-impregnated on HY can increase the hydrogenation capability of the catalyst and simultaneously lower the acidity of the support. The results show that the coordination of high hydrogenation capability and low acidity of catalyst can inhibit the formation of secondary cracking on some extent, and increase the selectivity of diesel. While Ni/W metals supported on HY/Al2O3 can achieve a relative balance of hydrogenation and cracking, thus the catalysts have a higher activity and the more flexible ability to modulate reaction.

The effect of sulfate on Fischer-Tropsch synthesis performance was investigated in a slurry- phase continuously stirred tank reactor (CSTR) over a Fe-Mn catalyst. The physiochemical properties of the catalyst impregnated with different levels of sulfate were characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR), Møssbauer spectroscopy, and CO2 temperature-programmed desorption (TPD). The characterization results indicated that the impregnated sulfate slightly decreased the BET surface area and pore volume of the catalyst, suppressed the catalyst reduction and carburization in CO and syngas, and decreased the catalyst surface basicity. At the same time, the addition of small amounts of sulfate improved the activities of Fischer- Tropsch synthesis (FTS) and water gas shift (WGS), shifted the product to light hydrocarbons (C1–C11) and suppressed the formation of heavy products (C12+). Addition of SO2−4 to the catalyst improved the FTS activity at a sulfur loading of 0.05–0.80 g per 100 g Fe, and S-05 catalyst gave the highest CO conversion (62.3%), and beyond this sulfur level the activity of the catalyst decreased.

•Two 4000 bbl/d demonstration scale projects using the MTFT technology are being successfully operated in China.•DFT studies on adsorption and reaction mechanisms on iron phases can provide guidance to development of F–T catalysts.•Kinetics based on theoretical and experimental results can be very important tools for F–T reactor and process development.Recent advance using Synfuels China's Fischer–Trospch (F–T) synthesis technology has been made in the 4000 bbl/d coal-to-liquids (CTL) plants in China. Fundamental studies with more than twenty years solid data and experience accumulation in catalysis and kinetic studies have paved the way to the successful demonstration of Synfuels China's medium temperature FT (MTFT) synthesis process. Density Functional Theory (DFT) together with the sophisticated catalyst property characterization tools has been routinely applied during catalyst development. Fundamental R&D efforts integrating all aspects of chemical engineering have greatly been enhanced by combining the fundamental tools covering the F–T synthesis mechanism, reaction engineering, and process optimization.

The modification of Fe–SiO2 interaction in iron catalysts for Fischer–Tropsch synthesis (FTS) by the incorporation of ZrO2 was investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction, powder X-ray diffraction, transmission electronic microscopy, and Mössbauer spectroscopy. The results indicated that the strong Fe–SiO2 interaction could be explained in terms of the formation of Fe–O–Si bonds between iron and SiO2, and these bonds were effectively weakened by ZrO2, which consequently enhanced the reduction and carburization of the catalyst and improved the stability of the iron carbides formed. FTS performances, tested in a fixed-bed reactor, showed that both the activity and the C5+ selectivity of the Zr-modified catalysts first increased, passed a maximum at Zr loading of 100Fe/20SiO2–20ZrO2 with increasing zirconia, and then decreased dramatically at higher Zr loadings. The acid content in the water phase decreased, while the alcohol content increased with the addition of zirconia.Graphical abstractFTIR results show that Fe–SiO2 interaction could be well explained in terms of the formation of Fe–O–Si bond, and this interaction can be weakened by ZrO2.Download high-res image (74KB)Download full-size imageResearch highlights► The Fe–SiO2 interaction could be explained in terms of the formation of Fe–O–Si bond. ► The strong Fe–SiO2 interaction could be weakened by ZrO2. ► The added ZrO2 improved the stability of iron carbides in terms of H2O oxidation.► The Fischer–Tropsch synthesis performance was improved by the addition of ZrO2.

Atomic layer deposition (ALD) was applied to deposit Pt into KL zeolite channels. The location of Pt deposition and the interaction between Pt and the KL zeolite have been investigated by various characterization methods as well as DFT simulations. It has been demonstrated that Pt nanoparticles (NPs) with precisely controlled size (∼0.8 nm) and high dispersion have been successfully deposited into the micropores of the KL zeolite. The produced Pt/KL catalysts exhibited highly efficient performance for n-heptane reforming to aromatics with a high toluene selectivity up to 67.3% (toluene/total aromatics = 97.8%) and a low methane selectivity (0.9%), in spite of an ultralow Pt loading (0.21 wt%). It was revealed that the strong interaction between Pt and the KL zeolite resulting in the electron-enriched state of Pt and the confinement of Pt in the micropores of the KL zeolite facilitated the aromatization of n-heptane. The small size and high dispersion of Pt NPs contributed to inhibition of the hydrogenolysis reaction. Prevention of agglomeration of Pt NPs due to confinement inside the micropores of the KL zeolite and the strong interaction led to the high stability of the Pt/KL catalysts.

Atomic layer deposition (ALD) was applied to deposit Pt into KL zeolite channels. The location of Pt deposition and the interaction between Pt and the KL zeolite have been investigated by various characterization methods as well as DFT simulations. It has been demonstrated that Pt nanoparticles (NPs) with precisely controlled size (∼0.8 nm) and high dispersion have been successfully deposited into the micropores of the KL zeolite. The produced Pt/KL catalysts exhibited highly efficient performance for n-heptane reforming to aromatics with a high toluene selectivity up to 67.3% (toluene/total aromatics = 97.8%) and a low methane selectivity (0.9%), in spite of an ultralow Pt loading (0.21 wt%). It was revealed that the strong interaction between Pt and the KL zeolite resulting in the electron-enriched state of Pt and the confinement of Pt in the micropores of the KL zeolite facilitated the aromatization of n-heptane. The small size and high dispersion of Pt NPs contributed to inhibition of the hydrogenolysis reaction. Prevention of agglomeration of Pt NPs due to confinement inside the micropores of the KL zeolite and the strong interaction led to the high stability of the Pt/KL catalysts.