燃料化学学报最新文献

Abstract

A series of Cu_xCo_3–xAl hydrotalcite-like catalysts with different Cu/Co molar ratios were synthesized by the urea homogeneous precipitation method and used for the direct hydrogenation-hydrogenolysis of furfural to 1,5-pentanediol. The results showed that the Cu/Co molar ratio of the catalyst had a significant effect on its textural properties and catalytic performance. The catalyst exhibited excellent catalytic performance when the molar ratio of Cu/Co was 1:29 (Cu_0.1Co_2.9Al), and the conversion of furfural was 100% together with 51.1% yield of pentanediol among which the yield of 1,5-pentanediol was 41.1%, under the reaction condition of 140 °C, 4 MPa H₂ for 6 h. Extensive characterization techniques, including temperature-programmed reduction (H₂-TPR), temperature-programmed desorption (H₂-TPD), X-Ray photoelectron spectroscopy (XPS) and Raman confirmed that the excellent catalytic activity of Cu_0.1Co_2.9Al catalyst was attributed to the highest content of Cu⁰ and CoO_x on its surface, and a synergistic catalytic effect was present between them. Typically, Cu⁰ was used to adsorb and activate H₂, and CoO_x with much oxygen vacancies promoted the adsorption and activation of C=O groups in furfural molecules, leading to the quick conversion of furfural to furfuryl alcohol. In addition, the oxygen vacancies anchored the –OH in the intermediate furfuryl alcohol to produce a C2-terminal oblique adsorption on the catalyst surface. Then it promoted the hydrogenation of C2=C3 with the weakening and cleavage of C2–O1 bond, and enhanced the selectivity of 1,5-pentanediol.

Abstract

The Pr_xZr_1–xO_2–δ catalyst with different atom ratio of Pr/Zr was prepared by the sol-gel to catalytic oxidation denitration. Results showed that the efficiency of catalytic oxidation denitration increased initially and decreased afterward with the ratio of Pr atom increased. And the optimum denitration activity could achieve 94.62% at 250 °C when the atom ratio of Pr/Zr was 5:5. The catalysts were characterized by SEM, N₂ adsorption-desorption, XRD, XPS, H₂-TPR, and FT-IR. The results illustrated that the catalyst (Pr_0.5Zr_0.5O_2–δ) with the best activity has a “layered” morphology, many pores on the surface, and it has a large specific surface area and pore volume of 77.74 m²/g and 0.66 cm³/g, respectively. Furthermore, the crystalline phase transforms from c-ZrO₂ to Pr₂Zr₂O₇ with the increasing of Pr atom. XPS and H₂-TPR results showed that the surface chemosorption oxygen and surface Pr⁴⁺ oxides increased, and the rising of Pr atom ratio was beneficial to produce oxygen vacancy (Vӧ) site which advantageous to improve the efficiency of catalytic oxidation denitration. FT-IR characterization results indicated that Pr_0.5Zr_0.5O_2–δ solid solution had better NO selectivity, which was conducive to the catalytic oxidation of NO. The anti-SO₂ and H₂O toxicity experiments showed that Pr/Zr atomic ratio at 5:5 had better anti-toxicity than other ratios. In addition, using IC to analysis absorption products, the result showed that${\text{NO}}_{\text{2}}^{–}$ and${\text{NO}}_{\text{3}}^{–}$ were the main products in the absorption solution.

Abstract

Ammonia borane (AB) is considered to be a promising chemical hydrogen storage material with high hydrogen storage density (19.6%), which can release three molar equivalents of hydrogen through catalytic hydrolysis at room temperature. However, AB releases hydrogen slowly in water, it is necessary to develop highly active metal nanocatalysts to accelerate the process of hydrolysis. This article provides an overview of the synthesis and characterization methods of ammonia borane, the mechanism of hydrolysis and catalytic hydrogen production using the unique dihydrogen key in the ammonia borane structure, and the various factors that affect the hydrogen release performance of AB.

A catalytic slurry oil (SO) was treated by moderate pre-hydrotreating, and the structural compositions, the thermal stability, the distillate oil yield, and the coking behavior of SO before and after hydrotreating were analyzed. The carbonization performance as well as the co-carbonization performance of the middle distillate (350–500 °C) and the high boiling point distillate (500–550 °C) derived from the hydrogenated SO (HSO) were investigated. The results show that the content of naphthenes and hydrogenated aromatics of HSO increases, while the olefin content decreases, and the olefinic hydrogen content of HSO decreases from 2.71% to 0.97%. Thus, the thermal stability of HSO is fundamentally improved. Additionally, compared with SO, the yields of the middle distillate and the high boiling point distillate of HSO increased by 25.8% and 23.1%, respectively. More importantly, there is no significant coke formation during distillation of HSO. The carbonization experimental results show that the anisotropic textural structure of the coke obtained from the middle distillate derived from HSO is the large flow domain structure, and the coke has the lowest coefficient of thermal expansion (CTE) value of 2.25×10⁻⁶ °C⁻¹. The carbonization performance of the high boiling point distillate derived from HSO is poor, while the co-carbonization with the middle distillate significantly improves the carbonization performance of the high boiling point distillate. The anisotropic textural structure of the coke derived from carbonization of combined fraction is the large flow domain structure and the CTE value is less than 2.30×10⁻⁶ °C⁻¹, when the mass ratio of aromatic fraction to middle fraction is not higher than 2:1.

A series of Ca-Zr catalysts modified by different transition metals were prepared by the sol-gel method and their catalytic performance in the synthesis of dimethyl carbonate (DMC) from methanol and propylene carbonate (PC) by transesterification at low temperature was investigated. The results indicate that the selectivity to DMC of various transition metal-modified Ca-Zr catalysts follows the order of Co-Ca-Zr > Cu-Ca-Zr > Ca-Zr > Fe-Ca-Zr > Ni-Ca-Zr > Zn-Ca-Zr. For the transesterification over the Co-Ca-Zr catalyst, in particular, the conversion of PC reaches 84.3% with a selectivity of 94.5% to DMC after reaction for 2 h under 35 °C, a methanol/PC molar ratio of 15, and catalyst amount of 4%. Combining with the XRD, FT-IR, XPS and CO₂-TPD results, it is revealed that increasing the strength of basic sites can raise the conversion of PC, whereas increasing the density of basic sites leads to a decrease of the selectivity to DMC. As a result, the Co-modified Ca-Zr (Co-Ca-Zr) catalyst, with the lowest density of surface basic sites but the highest fraction of strong basic sites, exhibits a high conversion of PC and a high selectivity to DMC for the transesterification of PC with methanol at a low temperature.

In this study, coal tar-based phenolic foam (CPF) was prepared using low-temperature coal tar as raw material to partially replace phenol. The chemical structure, apparent morphology, compressive strength, thermal stability, flame retardancy and thermal insulation properties of CPFs were characterized. The results show that CPFs have similar chemical structures to conventional phenolic foam. Comparing with conventional phenolic foam, the compressive strength of 30%CPF and 40%CPF increases by 18.3% and 55.9%, and the pulverization rate decreases by 22.9% and 50.8%, respectively. The results indicated that toughness was significantly strengthened due to the incorporation of aliphatic structures such as alkylphenols. In addition, the thermal stability of CPFs in the low temperature stage also improves. Although the limited oxygen index of CPFs decreases and thermal conductivity of CPFs increases, they still maintain good flame retardancy and thermal insulation properties. The obtained results prove that low-temperature coal tar can significantly replace phenol to prepare phenolic foam with good performance, which provides a new idea for the high-value utilization of low-temperature coal tar.

The Cu-M/ZnO catalysts (M = Zr⁴⁺, Al³⁺ and Mg²⁺) for dimethyl oxalate (DMO) selective hydrogenation to ethylene glycol (EG) were synthesized by the co-precipitation method. The properties of the as-synthesized catalysts were characterized by N₂-physisorption, N₂O-titration, XRD, H₂-TPR, CO₂-TPD, SEM, FT-IR and XPS. It was found that the Cu dispersion could be effectively promoted by the dopants incorporated in the Cu/ZnO catalyst. Particularly, a trace amount of Mg²⁺ and Al³⁺ dopants could significantly reinforce the chemical interaction between the Cu and ZnO phases by embedding into the ZnO lattice, while the Cu/ZrO₂ interaction could be improved with the introduction of Zr⁴⁺. For DMO gas-phase hydrogenation, the EG yield of the Cu/ZnO catalyst increased from 75.0% to 85.0% and 90.0% in the presence of Zr⁴⁺ and Al³⁺ dopants, respectively. Particularly, the EG selectivity of Cu-Mg/ZnO catalyst reached up to 95.0% with DMO completely converted for more than 100 h. The correlation between the catalytic behavior and physicochemical features of the Cu/ZnO based catalysts suggested that the surface Cu⁺ sites was vital for the catalytic behavior with adequate Cu⁰ sites. Additionally, the strengthened Cu/oxide interaction favored the outstanding stability of the Cu-Zr/ZnO and Cu-Mg/ZnO catalyst for DMO hydrogenation.

The effects of KCl-ZnCl₂ molten salt on the pyrolysis characteristics and pyrolysis products of heavy bio-oil at 400, 500 and 600 °C were studied. The results showed that molten salt increased the solid yield of heavy bio-oil pyrolysis and decreased the gas yield. Some compounds such as phenol, cresol, ethylphenol and 4-propylphenol had good enrichment effect, especially the relative concentration of cresol increased from 8.82% to 20.85% at 400 °C, while the relative concentration of phenol increased from 2.18% to 8.62% at 600 °C. During formation of char, molten salt reduced the content of carbon and increased the content of oxygen, increased the BET surface area and total pore volume of pores. Molten salt promoted formation of pore structure of the solid product and increased its average pore diameter.

A series of metal oxide catalysts were prepared by impregnating Cu, Mn, Fe, Ce and Ti on ZSM-5 molecular sieve. The physicochemical properties of the catalysts were characterized by SEM, XRD, N₂ adsorption/desorption, XPS, H₂-TPR, and the catalytic oxidation of toluene was investigated. The results showed that Cu/ZSM-5 had rough surface, uniform distribution of metal, good pore structure, superior low-temperature reducibility and abundant adsorbed oxygen species. Cu/ZSM-5 with 5% loading exhibited excellent catalytic activity for toluene oxidation and the best sulfur resistance performance, with t₉₀ (GHSV=24000 h⁻¹) being 224 °C in SO₂ environment. In-situ DRIFTS experiments revealed that the degradation path of toluene was as follows: toluene was first adsorbed on the surface of the catalyst to form adsorbed toluene, then it was converted into benzaldehyde and benzoic acid successively on the catalyst. And small molecule organics such as maleic acid and carboxylic acid were formed through ring opening reaction, and finally was oxidized to CO₂ and H₂O.

A series of Cu(x)/Hβ catalysts were prepared by the impregnation method and the effect on the performance of the catalysts for the selective catalytic reduction of NO with NH₃ (NH₃-SCR) was investigated. Characterization techniques such as XRD, N₂ adsorption-desorption, NH₃-TPD, NO-TPD, H₂-TPR, EDS and XPS were used to investigate the physical and chemical properties of the catalysts and the reason of the decrease of catalyst activity in the presence of SO₂. It was shown that the catalyst Cu(3)/Hβ, the Cu loading was 3% and Cu(2)/Hβ, the Cu loading was 2%, exhibited the better catalytic activity when the initial reaction material contained no SO₂ and SO₂, and t₉₅ was 169 and 225 °C, respectively. The analysis results of the catalyst before and after the reaction showed that the main reason for the decrease of catalyst activity in the presence of SO₂ was that the ammonium sulfur salt which was formed by the reaction of SO₂ and NH₃ in the low reaction temperature covers the catalyst active center.