Journal of Natural Gas Chemistry最新文献

Ba_0.5Sr_0.5Co_0.8Fe_0.1Ni_0.1O_3-δ(BSCFNiO) perovskite oxides were synthesized using a combined EDTA-citrate complexation method, and then pressed into disk and applied in a membrane reactor. The performance of the BSCFNiO membrane reactor was studied for partial oxidation of methane over Ni/a-Al₂O₃ catalyst. The time dependence of oxygen permeation rate and catalytic performance of BSCFNiO membrane during the catalyst initiation stage were investigated at 850°C. In unsteady state, oxygen permeation rate, methane conversion and CO selectivity were closely related to the state of the catalyst. After 300 min from the initial time, the reaction condition reached to steady state and oxygen permeation rate were obtained about 11.7cm³·cm⁻²·min⁻¹. Also, the performance of membrane reactor was studied at the temperatures between 750 and 950°C. The results demonstrated good performance for the membrane reactor, as CH₄ conversion and CO selectivity permeation rate reached 98% and 97.5%, respectively, and oxygen permeation rate was about 14.5 cm³·cm⁻²·min⁻¹ which was 6.8 times higher than that of air-helium gradient. Characterization of membrane surface by SEM after reaction showed that the original grains disappeared on both surfaces exposed to the air and reaction side, but XRD profile of the polished surface membrane indicated that the membrane bulk preserved the perovskite structure.

Performance of the oxidative coupling of methane in fluidized-bed reactor was experimentally investigated using Mn-Na₂WO₄/SiO₂, La₂O₃/CaO and La₂O₃-SrO/CaO catalysts. These catalysts were found to be stable, especially Mn-Na₂WO₄/SiO₂ catalyst. The effect of sodium content of this catalyst was analyzed and the challenge of catalyst agglomeration was addressed using proper catalyst composition of 2%Mn-2.2%Na₂WO₄/SiO₂. For other two catalysts, the effect of Lanthanum-Strontium content was analyzed and 10%La₂O₃–20%SrO/CaO catalyst was found to provide higher ethylene yield than La₂O₃/CaO catalyst. Furthermore, the effect of operating parameters such as temperature and methane to oxygen ratio were also reviewed. The highest ethylene and ethane (C₂) yield was achieved with the lowest methane to oxygen ratio around 2. 40.5% selectivity to ethylene and ethane and 41% methane conversion were achieved over La₂O₃-SrO/CaO catalyst while over Mn-Na₂WO₄/SiO₂ catalyst, 40% and 48% were recorded, respectively. Moreover, the consecutive effects of nitrogen dilution, ethylene to ethane production ratio and other performance indicators on the down-stream process units were qualitatively discussed and Mn-Na₂WO₄/SiO₂ catalyst showed a better performance in the reactor and process scale analysis.

A novel design of plate-type microchannel reactor has been developed for fuel cell-grade hydrogen production. Commercial Cu/Zn/Al₂O₃ was used as catalyst for the reforming reaction, and its effectiveness was evaluated on the mole fraction of products, methanol conversion, hydrogen yield and the amount of carbon monoxide under various operating conditions. Subsequently, 0.5 wt% Ru/Al₂O₃ as methanation catalyst was prepared by impregnation method and coupled with MSR step to evaluate the capability of methanol processor for CO reduction. Based on the experimental results, the optimum conditions were obtained as feed flow rate of 5 mL/h and temperature of 250°C, leading to a low CO selectivity and high H₂ yield. The designed reformer with catalyst coated layer was compared with the conventional packed bed reformer at the same operating conditions. The constructed fuel processor had a good performance and excellent capability for on-board hydrogen production.

Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal. Thus in this paper, we embark on a systematic study for Pd_n (n = 1–5) clusters adsorbed on TiO₂(110) surface based on DFT-GGA calculations utilizing periodic supercell models. A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction, while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface. According to the transition states (TSs) search, the adsorbed Pd trimer tends to triangular growth mode, rather than linear mode, while the Pd₄ and Pd₅ clusters prefer three-dimensional (3D) models. However, the oxygen vacancy has almost no influence on the promotion of Pd_n cluster nucleation. Additionally, of particular significance is that the Pd-TiO₂ interaction is the main driving force at the beginning of Pd nucleation, whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger. It is hoped that our theoretical study would shed light on further designing high-performance TiO₂ supported Pd-based catalysts.

Different from the classical configuration CuO/CeO₂ catalyst, the inverse configuration CeO₂/CuO catalyst (atomic ratio of Ce/Cu = 10/100) was prepared by impregnation method. Five calcination temperatures were selected to investigate the interaction between CeO₂ and CuO support. It is found that as calcination temperature increased from 500 to 900°C, sintering of CeO₂ particles on the support occurred together with the diffusion of a portion of Ce⁴⁺ ions into CuO crystals, forming solid solution. Formation of interface complex Ce-O-Cu was suggested by TPR measurements. The catalyst calcined at 700°C gives the highest activity for preferential oxidation of CO in excess H₂ stream.

ZnO could be a suitable catalyst for the oxidative conversion of CH₄, C₂H₆ and C₃H₈. However, the main drawback is its thermal instability. Therefore, ZnO supported on ZrO₂, TiO₂, γ-Al₂O₃ and SiO₂ was investigated for the oxidative dehydrogenation of propane and ethane, and the oxidative coupling of methane. The stability of the supported ZnO is partially improved, but ZnO reacts with the support material, forming new compounds (Zn-zirconates, -titanates, -aluminates and -silicates), which already occurs below reaction temperature. This might also be the case for many other heterogeneous catalysts.

An extensive study of Fischer-Tropsch (FT) synthesis on cobalt nano particles supported on γ-alumina and carbon nanotubes (CNTs) catalysts is reported. 20 wt% of cobalt is loaded on the supports by impregnation method. The deactivation of the two catalysts was studied at 220°C, 2 MPa and 2.7 L/h feed flow rate using a fixed bed micro-reactor. The calcined fresh and used catalysts were characterized extensively and different sources of catalyst deactivation were identified. Formation of cobalt-support mixed oxides in the form of xCoO·yAl₂O₃ and cobalt aluminates formation were the main sources of the Co/γ-Al₂O₃ catalyst deactivation. However sintering and cluster growth of cobalt nano particles are the main sources of the Co/CNTs catalyst deactivation. In the case of the CO/γ-Al₂O₃ catalyst, after 720 h on stream of continuous FT synthesis the average cobalt nano particles diameter increased from 15.9 to 18.4 nm, whereas, under the same reaction conditions the average cobalt nano particles diameter of the Co/CNTs increased from 11.2 to 17.8 nm. Although, the initial FT activity of the Co/CNTs was 26% higher than that of the CO/γ-Al₂O₃, the FT activity over the Co/CNTs after 720 h on stream decreased by 49% and that over the CO/γ-Al₂O₃ by 32%. For the CO/γ-Al₂O₃ catalyst 6.7% of total activity loss and for the Co/CNTs catalyst 11.6% of total activity loss cannot be recovered after regeneration of the catalyst at the same conditions of the first regeneration step. It is concluded that using CNTs as cobalt catalyst support is beneficial in carbon utilization as compared to γ-Al₂O₃ support, but the Co/CNTs catalyst is more susceptible for deactivation.

Zn-based sorbent (Z20SC) prepared through semi-coke support in 20 wt% zinc nitrate solution by high-pressure impregnation presents an excellent desulfurization capacity in hot coal gas, in which H₂S can not be nearly detected in the outlet gas before 20 h breakthrough time. The effects of the main operational conditions and the particle size of Z20SC sorbent on its desulfurization performances sorbent were investigated in a fixed-bed reactor and the desulfurization kinetics of Z20SC sorbent removing H₂S from hot coal gas was calculated based on experimental data. Results showed that the conversion of Z20SC sorbent desulfurization reaction increased with the decrease of the particle size of the sorbent and the increases of gas volumetric flow rate, reaction temperature and H₂S content in inlet gas. Z20SC sorbent obtained from hydrothermal synthesis by high-pressure impregnation possessed much larger surface area and pore volume than semi-coke support, and they were significantly reduced after the desulfurization reaction. The equivalent grain model was reasonably used to analyze experimental data, in which k_s = 4.382×10⁻³ exp(−8.270×10³/R_gT) and D_ep = 1.262×10⁻⁴exp(−1.522×10⁴/R_gT). It suggests that the desulfurization reaction of the Z20SC sorbent is mainly controlled by the chemical reaction in the initial stage and later by the diffusion through the reacted sorbent layer.

The equilibrium hydrate formation conditions for CO₂/H₂ gas mixtures with different CO₂ concentrations in 0.29 mol% TBAB aqueous solution are firstly measured. The results illustrate that the equilibrium hydrate formation pressure increases remarkably with the decrease of CO₂ concentration in the gas mixture. Based on the phase equilibrium data, a three stages hydrate CO₂ separation from integrated gasification combined cycle (IGCC) synthesis gas is investigated. Because the separation efficiency is quite low for the third hydrate separation, a hybrid CO₂ separation process of two hydrate stages in conjunction with one chemical absorption process (absorption with MEA) is proposed and studied. The experimental results show H₂ concentration in the final residual gas released from the three stages hydrate CO₂ separation process was approximately 95.0 mol% while that released from the hybrid CO₂ separation process was approximately 99.4 mol%. Thus, the hybrid process is possible to be a promising technology for the industrial application in the future.

In this work, experimental studies of biomass gasification under different operating conditions were carried out in an updraft gasifier combined with a copper slag reformer. The influence of gasification temperature, equivalence ratio (ER) and copper slag catalyst addition on gas production and tar yield were investigated. The experimental results showed that the content of H₂ and CO, gas yield and LHV increased, while the tar yield and the content of CO₂, CH₄ and C₂H_x in the gas product decreased with the temperature. At 800 °C, with the increase of ER, the LHV, the tar yield and the content of H₂, CO, CH₄ and C₂H_x in gas products decreased, while the gas yield and the content of CO₂ increased. Copper slag was introduced into the secondary reformer for tar decomposition. The Fe₃O₄ phase in the fresh copper slag was reduced to FeO (Fe²+) and metallic Fe by the gas product. Fe species (FeO and metallic Fe) acted as the active sites for tar catalytic decomposition. The catalytic temperature had a significant influence on tar conversion and the composition of the gas product. Typically, the tar conversion of about 17%–54% could be achieved when the catalytic temperature was varied from 750 to 950 °C. Also, the content of H₂ and CO increased with the catalytic temperature, while that of CO₂, CH₄ and C₂H_x in the gas product decreased. It was demonstrated that copper slag was a good catalyst for upgrading the gas product from biomass gasification.