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.

A systematic study was undertaken to investigate the effects of the addition of nickel on the bulk phase composition and reduction/carburization behaviors of a Fe–Ni bimetallic catalyst. The catalyst samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H2 (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was measured at 1.5 MPa, 250 °C and syngas with H2/CO ratio of 2.0. The characterization results indicated that the fresh nickel-promoted catalysts are mainly composed of α-Fe2O3 and NiFe2O4. The addition of nickel improves the dispersion of iron oxides and decreases the crystallite size of metal oxides. The presence of nickel increases the rates of reduction and carburization in H2 and CO, respectively, while suppresses the formation of the iron carbides in the syngas reduction. The incorporation of nickel improves the selectivity to methane and suppresses the formation of heavy hydrocarbons (C5 +). The catalyst with high nickel content has a high selectivity to methane and low selectivity to heavy hydrocarbons (C5 +).

A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO2 catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H2 (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe2O3 and Fe3O4, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe2O3 in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe3O4 in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe3+/Fetotal = 1.0) has the highest CO conversion, whereas Fe-03 (Fe3+/Fetotal = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C1–C4) and low selectivity to heavy hydrocarbons (C5+).

The effects of Cu and K promoters on precipitated iron-based Fischer–Tropsch synthesis (FTS) catalysts were investigated by using N2 physical adsorption, temperature-programmed reduction/desorption (TPR/TPD) and Mössbauer effect spectroscopy (MES). The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that Cu promoter facilitates the high dispersion of Fe2O3, significantly promotes the reduction and H2 adsorption, but severely suppresses CO adsorption and the carburization. However, K promoter severely retards the reduction and suppresses the H2 adsorption, facilitates the CO adsorption and promotes the carburization. In the FTS reaction, it was found that Cu promoter decreases the FTS initial activity and water gas shift (WGS) reaction activity, promotes the oxidation of iron carbides to Fe3O4 and accelerates the deactivation of iron-based catalyst. However, K promoter improves the FTS activity and WGS reaction activity, suppresses the oxidation of iron carbide to Fe3O4 and significantly improves the stability of iron-based catalyst. As compared with individual promotion of Cu or K, the double promotions of Cu and K significantly improve the FTS and WGS activities and keep excellent stability. Due to weaker CO adsorption and stronger H2 adsorption than the catalysts without Cu, Cu promoted catalysts have higher selectivity to light hydrocarbons and methane and lower selectivity to heavy hydrocarbons. However, the opposite result is obtained on the catalyst incorporated with K promoter.The activity and stability of the catalysts. Reaction condition: 260 °C, 1.5 MPa, H2/CO = 0.67 and GHSV = 1000 h−1. The addition of Cu promoter into iron-based catalyst decreases the catalyst activity and accelerates the deactivation of iron-based catalyst. The addition of K and the co-promotional effects of Cu and K not only increase the catalyst activity, but also improve the catalyst stability.

The phase transformations and textural properties were systematically investigated over an unpromoted iron Fischer–Tropsch synthesis (FTS) catalyst prepared from ferrous sulfate with different Fe3+/Fetotal ratios at different preparation stages (precipitation, dryness and calcination). The catalyst samples were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy and N2 physisorption. The characterization studies show that after precipitation the samples are composed of α-FeOOH, Fe3O4 and α-Fe2O3. The content of Fe3O4 increases with the increase of Fe3+/Fetotal ratio (Rm) and reaches the maximum content at the Rm of 0.72. There is not a significant phase transformation during the dryness of the catalyst samples. After being calcined at 500 °C for 5 h, α-FeOOH and Fe3O4 existed in the catalyst samples are transformed into α-Fe2O3. The characterization results from N2 physisorption show that when the Rm of sample is 0.72, the BET surface area and pore volume have the maximum values (26 m2/g, 0.21 cm3/g) after the samples being calcined at 500 °C.

Calcination behaviors play an important role in Fischer–Tropsch (FT) performance over a slurry iron–manganese catalyst. The present study was undertaken to investigate the effects of calcination behaviors (calcination temperature, heating rate and calcination atmosphere) on the textural properties, reduction/carburization behavior, bulk phase structure and FT synthesis performances over precipitated Fe–Mn catalysts. N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2 thermal gravimetric analysis (TGA) and Mössbauer effect spectroscopy (MES) were used to characterize the catalyst. It is found that increasing calcination temperature and heating rate lead to low surface area and high enrichment of Mn on the catalyst surface. High calcination temperature also increased the crystallite size of α-Fe2O3 and suppressed the reduction/carburization of the catalysts in H2 and syngas. Low calcination temperature and low heating rate promoted the further carburization of the catalyst and increased the activity during FT process. High calcination temperature and low heating rate restrained the formation of CH4, increases C5+ selectivity and improved the selectivity to light olefins. In addition, calcination in argon could improve the carburization and increase FT activity of the catalyst. The present iron–manganese catalyst with lower calcination temperature, lower heating rate and calcined in argon is optimized for its FT performances.

The effects of manganese promoter on the reduction–carburization behavior, surface basicity, bulk phase structure and their correlation with Fischer-Tropsch synthesis (FTS) performances have been emphatically studied over a series of spray-dried Fe–Mn–K catalysts with a wide range of Mn incorporation amount. The catalysts were characterized by means of H2 and CO temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), Mössbauer spectroscopy etc.. The results indicated that small amount of Mn promoter can promote the reduction of the catalyst in H2. However, FeO phase formed during reduction is stabilized by MnO phase with the further increase of Mn content, making FeO phase difficult to be reduced in H2. The addition of Mn promoter can stabilize the Fe2+ and Fe3+ ions, and suppresses the reduction and carburization of the catalyst in syngas and CO. Mn promoter can also enhance the amount of the basic sites and weaken the strength of the basic sites, which possibly come from the reason that the Mn–K interaction is strengthened with the addition of Mn promoter. The change of surface basicity can modify the selectivity of hydrocarbons and olefins, and the change of bulk structure phase derived from the addition of Mn promoter will affect the catalyst activity and run stability. The synergetic effects of the two main factors result in an optimized amount of Mn promoter for the highest catalyst activity and heavy hydrocarbon selectivity in slurry FTS reaction of Fe–Mn–K catalysts.

The effects of copper and potassium on the activity and selectivity of coprecipitated Fe-Mn/SiO2 catalysts for Fischer-Tropsch synthesis (FTS) were studied in a slurry phase continuous stirred tank reactor. The reduction and adsorption behaviors of the catalysts were investigated using temperature-programmed reduction/temperature-programmed desorption (TPR/TPD) methods. It was found that copper improves the reduction of the catalyst in H2 or CO. Potassium improves the reduction of the catalyst in CO, whereas it suppresses the reduction of the catalyst in H2. Copper enhances the H2 adsorption, whereas potassium has no influence on the H2 adsorption. In the FTS reaction, copper shortens the induction period required for reaching the steady state activity, whereas potassium prolongs the induction period. The potassium promoter increases the activity and decreases the selectivity of methane. The promotion effects of Cu and K on the activity and selectivity is more obvious than that of Cu, that is, the activity is higher and the methane selectivity is lower on the doubly promoted catalyst.

Methanolytic depolymerization of polyethylene terephthalate (PET) was carried out in a stainless stirred autoclave at temperatures of 523–543 K, pressures of 8.5–14.0 MPa, and with a weight ratio of methanol to PET from 3 to 8. The solid products mainly composed of dimethyl terephthalate and small amounts of methyl-(2-hydroxyethyl) terephthalate, bis (hydroxyethyl) terephthalate, dimers and oligomers were analyzed by high performance liquid chromatography (HPLC). The liquid products composed of ethylene glycol and methanol were analyzed by gas chromatography (GC). It was found that both the yield of dimethyl terephthalate and the degree of PET depolymerization were seriously influenced by the temperature, weight ratio of methanol to PET, and reaction time, whilst the pressure has insignificant influence when it is above the critical point of methanol. The optimal depolymerization conditions are temperature of 533–543 K, pressure of 9.0–11.0 MPa, and the weight ratio (methanol to PET) from 6 to 8. The depolymerization of several PET wastes collected from the Chinese market was investigated under the optimal conditions.

A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors, and surface basicity of an iron-based Fischer-Tropsch synthesis (FTS) catalyst. The catalyst samples were characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), and Mössbauer spectroscopy. The FTS performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the manganese promoter incorporated by using the coprecipitation method could improve the dispersion of iron oxide, and decrease the size of the iron oxide crystallite. The manganese incorporated with the impregnation method is enriched on the catalyst's surface. The manganese promoter added with the impregnation method suppresses the reduction and carburization of the catalyst in H2, CO, and syngas because of the excessive enrichment of manganese on the catalyst surface. The catalyst added manganese using the coprecipitation method has the highest CO conversion (51.9%) and the lowest selectivity for heavy hydrocarbons (C12+).

AbstractA series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduc-tion/desorption (TPR/TPD) and Mossbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260 °C, 1.5 MPa, 1000 h−1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.