SSZ-13, a CHA-type aluminosilicate zeolite, has attracted substantial attention recently due to its extraordinary physicochemical properties, and Cu-modified SSZ-13 has been commercialized as a selective catalytic reduction (SCR) catalyst for controlling emissions from diesel engines. In this work, the Cu&Zn dual-metal-modified SSZ-13 zeolite catalyst (Cu&Zn-SSZ-13) was elegantly synthesized in a one-pot (OP) manner, and the prepared material exhibits good NH 3 -SCR activity. Impressively, Cu&Zn-SSZ-13(OP) has greater hydrothermal stability than Cu-SSZ-13 catalysts prepared by other means. The characterization data (obtained by XPS, H 2 -TPR, NH 3 -TPD and EPR techniques) in this work revealed that the Zn introduced by a one-pot method would not only help optimize and disperse the isolated Cu 2+ species, providing good SCR activity, but also form [Zn-OH]-Z, [Cu-O-Zn]-Z, and [Zn-O-Zn]-Z complexes. Further DFT calculations confirm that these complexes are much more stable than single Cu ions under hydrothermal aging, and these Zncontaining species can function as anchors to stabilize the SSZ-13 framework.
In this work, a priori COSMO-SAC model was combined with the original UNIFAC model, and thus the new COSMO-SAC-UNIFAC thermodynamic model with a strong predictive power for fluid phase equilibrium (VLE, LLE) was proposed. By this means the group binary parameter matrix of original UNIFAC model was extended by introducing the new 648 vacant parameter pairs for 51 main functional groups for the conventional substances in this work. Moreover, the combined thermodynamic model was first applied to process simulation on gas drying with ionic liquids (ILs). To verify the reliability of the COSMO-SAC-UNIFAC model, the predictive values were directly compared with experimental data coming from this work, our previous work, and literature. The moderately accurate predictions of the COSMO-SAC-UNIFAC model demonstrate the high potential applicability of this new model, especially for numerous systems with missing parameters including ILs, which are normally encountered in the original UNIFAC model.
Ionic liquids (ILs) as separating agents have been extensively studied in chemical separation processes. For IL-containing systems, the UNIFAC model for ILs (i.e., UNIFAC-Lei model) has become a popular group contribution approach to predict phase equilibrium behavior. Since the UNIFAC-Lei model was established in 2009, our group has continued to extend and revise this model because the accurate prediction and application scope of this model depend on the quality and size of the parameter matrix besides the statements and hypothesis assumed for the model. Thus, this work is focused on revising and extending the UNIFAC-Lei parameter matrix through plentiful and accurate experimental data. In this work, four new groups ([MIM][DBP], [MIM][TCM], [MIM][DCA], and [PYM][TCM]) were added, 63 pairs of new parameters were extended, and eight pairs of old parameters were revised. The COSMO calculation was used to get the unknown group surface area and volume parameters (R k and Q k ) of IL groups; the experimental phase equilibrium data of the systems containing ILs were used to get the unknown group binary interaction parameters (a nm and a mn ). The comparison of the UNIFAC-Lei predicted vapor–liquid equilibrium values with experimental data indicates that the UNIFAC-Lei model can provide relatively satisfactory phase equilibrium prediction for IL-containing systems.
In the present contribution, we investigate the catalytic cycle of the methane activation reaction over several copper sites by density functional theory calculation. Our results demonstrate that the C–H bond activation step is the rate-limiting step for all investigated copper sites. After C–H bond cleavage, different types of copper sites show different mechanisms for methane-to-methanol conversion. For the dioxygen copper sites, after the CH4 activation step, the CH3 radical is prone to react with the hydroxide group on the copper sites and form methanol directly. For the monooxygen copper sites, the CH3 radical is energetically favorable to adsorb on monooxygen copper sites, resulting in a stable methoxide. Then, a water molecule would react with the methoxide and form methanol with a negligible energy barrier (2.8 kcal/mol over [CuOCH3] and 3.3 kcal/mol over [Cu2OCH3]). Our results demonstrate that [CuO] sites are the most active for the C–H bond activation of methane, but their formation is predicted to be difficult from both the O2 and N2O methods. However, [Cu2O] sites can be readily formed through both the O2 and N2O methods, and they exhibit competitive activity for C–H activation. Increasing the [Cu2O] concentration in Cu-based zeolites is proposed as a feasible way to enhance the catalytic activity of Cu-ZSM-5.
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