燃料化学学报最新文献

A series of Cu/SiO₂ catalysts modified with lanthanum (La) (30Cu-nLa/SiO₂, n=0, 0.5, 1 and 2) were synthesized using the ethanol (EtOH)-assisted ammonia-evaporation method; their catalytic performance in the gas-phase hydrogenation of methyl acetate (MeOAc) to produce ethanol (EtOH) was investigated. The results indicate that the catalytic performance of Cu/SiO₂ can be greatly enhanced by La modification. In particular, the 30Cu-0.5La/SiO₂ catalyst exhibits excellent performance in the MeOAc hydrogenation; under 230 °C, 2 MPa H₂, an LHSV of 2 h^-1 and an H₂/MeOAc molar ratio of 20, the MeOAc conversion reaches 98.5%, with a total EtOH yield of 97.0%. The N₂-sorption, XRD, ICP-OES, H₂-TPR, FT-IR, TEM, XPS, and AES characterization results reveal that the introduced La metal has a strong interaction with Cu, which can promote the dispersion of the copper species on the SiO₂ support. Moreover, the content of Cu⁺ is increased significantly, which can enhance the electronic interaction with MeOAc via the acyl and methoxide groups and thus promote the hydrogenation of MeOAc to EtOH.

A series of Ce modified CuLDH-Ce_x catalysts were synthesized by adding different amounts of Ce to CuMgAl hydrotalcite (CuLDH) catalysts. The physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption-desorption (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. The results showed that the addition of Ce changed the hydrotalcite structure of CuLDH catalyst, and an appropriate amount of Ce increased the surface area of the catalyst and improved the dispersion of Cu particles. At the same time, an appropriate amount of Ce was beneficial for increasing the density of strong alkaline sites and the number of oxygen vacancies on the catalyst surface, promoting the adsorption and conversion of CO₂. Ce was beneficial for adjusting the Cu⁺/Cu⁰ ratio on the catalyst surface, and a higher Cu⁺/Cu⁰ ratio was conducive to the formation of methanol. When the Ce/Cu ratio was 0.3, the catalyst exhibited higher activity with 7.5% CO₂ conversion, 78.4% methanol selectivity and 362.8 g/(kg·h) spatiotemporal yield at 240 °C under 2.5 MPa with a GHSV=9000 mL/(g·h). It was proved by in-situ DRIFTS that CuLDH-Ce0.3 catalyst followed HCOO* reaction path during CO₂ hydrogenation for methanol.

The reasonable matching of zeolite and matrix is one of the most effective strategies to increase the yield of light olefins in naphtha catalytic cracking. However, the influence of the surface Lewis acidity within the matrix on the cracking reactions has remained ambiguous. Therefore, in present study, boron and zinc co-modified γ-Al₂O₃ and tin modified mesoporous silica KIT-6 with tuned surface Lewis acidity were applied to evaluate the cracking reactivity of n-heptane and 1-hexene to light olefins, in which the matrix was used alone and coupled with ZSM-5 zeolite in different packed modes. The effects of the modifiers on the textural properties and surface acidity of γ-Al₂O₃ and KIT-6 were investigated by XRD, TEM, N₂ physical absorption-desorption, and NH₃-TPD. The results showed that B doping reduced the Lewis acidity (both in the amount and acid strength) of γ-Al₂O₃, while the incorporation of Zn doping led to increased Lewis acidity. In addition, the Lewis acidity of ordered mesoporous KIT-6 increased as Sn doping rose. While for pure matrix, the ascend in conversions of n-heptane and 1-hexene was consistent with the increased Lewis acidity of the B and Zn co-modified γ-Al₂O₃ and xSn/KIT-6 rose, along with decreased activation energy. In contrast, when coupled with ZSM-5 zeolite, the highest conversion was achieved in the dual-bed manner of matrix and zeolite, and the conversion increased concomitantly with the increase in the Lewis acidity of the matrix. However, excessive Lewis acidity can accelerate the hydrogen transfer rate while diminishing the selectivity of light olefins.

To investigate the influence of pore structure on the catalytic activity of catalysts, four catalysts including three-dimensionally ordered macroporous-mesoporous (3DOM-m) CeTiO_x, three-dimensionally ordered macroporous (3DOM) CeTiO_x, three-dimensionally ordered mesoporous (3DOm) CeTiO_x and disordered mesoporous (DM) CeTiO_x were synthesized by the sol-gel method. The NH₃-SCR denitration testing results show that the performance of the catalysts with different pore structures follows the sequence of 3DOM-m CeTiO_x>3DOm CeTiO_x>3DOM CeTiO_x>DM CeTiO_x, and the 3DOM-m CeTiO_x shows an excellent catalytic activity, with more than 90% NO conversion in the range of 250–400 °C at a GHSV of 60000 h⁻¹. The characterization of catalysts by XRD, SEM, BET, NH₃-TPD and in-situ DRIFTS indicates that the surface area is not the dominant factor determining the catalytic activity of CeTiO_x. 3DOM-m CeTiO_x has a highly ordered macroporous-mesoporous structure and abundant Bronsted acidic sites, thereby improving the denitrification activity. The NH₃-SCR reaction over the 3DOM-m CeTiO_x mainly follows the L-H and E-R mechanisms.

Cu-Al spinel oxide as a sustained release catalyst gradually releases active metal Cu during the methanol steam reforming reaction, whose catalytic behavior depends strongly on the surface structure of the catalyst. In this context, Cu-Al spinel solid solution is synthesized by a solid phase ball milling method, followed by treating with acidic and basic solutions in order to modulate the surface composition and structure, thereby to further improve the catalytic performance. Nitric acid is effective for the removal of both surface dispersed Cu and Al oxide species, whereas sodium hydroxide is only effective for the removal of Al oxide species, and ammonium hydroxide shows the weakest effect, removing a very small amount of Cu and Al species. Accompanying with the loss of Cu and Al species, the catalyst surface undergoes structural reconstruction, showing a redistribution of Cu species. Consequently, the copper releasing behavior varies drastically. The catalytic testing results show that the nitric acid and ammonium hydroxide treated catalysts present improved activity, where in the former also shows better stability. Sodium hydroxide treatment has a negative effect on the sustained releasing catalytic performance. In combination with the characterization results of the tested catalysts, it is found that both the copper particle dimension and the microstructure strain of sustained released copper play important roles in the catalytic performance. The findings of this report provide a practical method for the improvement of the sustained releasing catalysis.

Carbon nitride (g-C₃N₄) prepared using thermal condensation of urea was pretreated by H₂O₂/NH₃·H₂O and used as support to obtain Fe/g-C₃N₄ catalyst via impregnation method. The catalytic performance of the catalysts both before and after modification was investigated in CO hydrogenation. Combining detailed characterizations, such as XRD, SEM, TEM, FT-IR, TG, CO₂-TPD, CO-TPD, H₂-TPR, contact angle measurement, and N₂ physical adsorption and desorption, we investigated the effects of surface pretreatment on the texture properties of Fe/g-C₃N₄ catalysts and the product distribution of CO hydrogenation. The results demonstrate that various pretreatment techniques have significant influences on the textural properties and catalytic performance of the catalysts. The prepared g-C₃N₄ with a typical honeycomb structure has strong interaction with highly dispersed Fe. Both before and after modification, the materials are hydrophilic, and the hydrophilicity is increased after treatment with H₂O₂ and NH₃·H₂O. Treatment with H₂O₂ enhances surface hydroxyl groups. NH₃·H₂O treatment improves surface amino groups, promotes CO adsorption, and facilitates the formation of Fe(NCN) phase. The surface basicity of all pretreated catalysts is enhanced. The water gas shift (WGS) reaction activity of the two-step modified catalyst Fe/AM-g-C₃N₄ was lower, and the CO₂ selectivity in CO hydrogenation was reduced to 11.61%. Due to the enhanced basicity of Fe/AM-g-C₃N₄, the secondary hydrogenation ability of olefins was inhibited to obtain higher olefin selectivity with C= 2–C= 4 of 32.37% and an O/P value of 3.23.

Catalytic combustion is an effective approach to remove volatile organic compounds, in which the development of highly active and durable catalyst is extremely crucial. Herein, a series of CuMnCe_x/Al₂O₃/cordierite monolithic catalysts were synthesized by using the ultrasonic-assisted impregnation method. The physicochemical properties were comprehensively characterized via the BET, XRD, SEM, EDX, H₂-TPR, O₂-TPD, XPS and EPR techniques. The results showed that the catalytic activity of CuMnCe_x/Al₂O₃/Cor for toluene combustion was strongly affected by the Ce content. The CuMnCe₂/Al₂O₃/Cor monolithic catalyst showed the best catalytic activity with toluene conversion of 90% at 263 °C under toluene concentration of 1 g/L and space velocity of 78000 mL/(g·h). Meanwhile, the well-dispersed CeO₂ in the CuMn matrix not only improved the content of oxygen vacancies and the mobility of oxygen species, but also enhanced the low-temperature reducibility of the catalyst. Moreover, the CuMnCe₂/Al₂O₃/Cor monolithic catalyst exhibited an excellent stability in the long-term test and cycle ability test.

A series of Mo/Sn (1:20, molar ratio) catalysts were prepared by two-step hydrothermal synthesis method, and the effect of calcination temperature of tin precursors on the reaction performance of methanol oxidation to dimethoxymethane (DMM) was investigated. The crystal structure, surface properties, redox property and valence change of molybdenum species of the catalyst were characterized by XRD, Raman, FT-IR, XPS, NH₃-TPD and H₂-TPR. The results showed that Mo1Sn20-600°CSn catalyst exhibited better performance than other catalysts, achieving DMM selectivity of 90% with methanol conversion of 30% at 140 °C. From the characterization results, the surface properties of the tin precursors affected the structure of catalyst, the degree of molybdenum oxide dispersion and valence of molybdenum species, and further influenced the performance of the catalysts. The high temperature calcination of tin precursors is more favorable for the generation of Mo⁶⁺ in the Mo1Sn20 catalyst.

To develop adsorbents suitable for the storage of natural gas by adsorption, activated carbon SAC-02, HKUST-1 and MIL-101(Cr) were synthesized and characterized in terms of structural morphology observation, nitrogen physisorption at 77.15 K, and methane adsorption at 293.15–313.15 K and 0–4 MPa. The methane adsorption isotherms were comparatively correlated with the Toth, D-A and Ono-Kondo equations and the performances of the adsorbent samples were evaluated in terms of the isosteric adsorption heat and the adsorbed phase density. The results indicate that, in comparison with the D-A and Ono-Kondo equations, the Toth equation displays much smaller relative errors in correlating the methane adsorption data and is more suitable for the adsorption equilibrium analysis on the adsorbed natural gas (ANG) system. MIL-101(Cr) exhibits the largest mean isosteric heat for methane adsorption and the density of the adsorbed phase of methane is smaller than that of the liquid methane but increases with the equilibrium pressure; overall, MIL-101(Cr) with the highest adsorption capacity is more suitable for methane adsorption than activated carbon and HKUST-1.

The selective catalytic reduction (SCR) NH₃ catalyst is mainly used in industrial production and automobile exhaust cleaning. In this study, a novel α%Fe₂O₃/ZrTiO₄ (α=0, 8, 12, 15) catalyst was prepared by the coprecipitation impregnation method. The results show that the NO_x conversion rate of 12%Fe₂O₃/ZrTiO₄ catalyst with the optimal composition is high above 80% at 250−400 °C, close to 100% at 300 °C, and N₂ selectivity is high above 90% at 200−450 °C. The redox properties, surface acidity, and O_β/(O_α + O_β) ratio of ZrTiO₄ catalysts are improved after loading Fe₂O₃ on the ZrTiO₄ surface, which is attributed not only to the porous structure of α%Fe₂O₃/ZrTiO₄ catalyst but also to the synergistic interaction between the active component Fe₂O₃ and the support ZrTiO₄. In addition, in-situ DRIFT reactions show that the NH₃-SCR reaction of 12%Fe₂O₃/ZrTiO₄ catalyst follows the Eley-Rideal mechanism. A clear reaction mechanism is conducive to a deeper understanding of the reaction process of NO_x conversion during SCR. This work provides a feasible strategy for Fe-based SCR catalysts to replace V-based catalysts in the medium temperature range in the future.