Density Functional Theory Studies on the Hydrolysis of Levoglucosenone to 5-Hydroxymethylfurfural.

Selective conversion of lignocellulosic biomass-derived chemicals is of critical significance for sustainable fine and commodity chemical industries. Cellulose-derived levoglucosenone (LGO) has a promising potential for producing 5-hydroxymethylfurfural (HMF) with a substantial yield under acid conditions, but the mechanism is unidentified. Herein, we disclose the mechanism of LGO conversion to HMF in the aqueous phase without and with H2SO4 as a catalyst by density functional theory (DFT) calculations for the first time. Results showed that LGO first forms 6,8-dioxabicyclo[3.2.1]-octane-2,4,4-triol (DH) via two sequential hydration reactions occurring at the C═C bond and then the ketone group. The use of H2SO4 as a catalyst significantly reduced the free energy barriers of LGO and DH conversion to HMF, with a free energy barrier of 115 kJ/mol for LGO → HMF compared to that of 91 kJ/mol for DH → HMF, demonstrating that DH is easier for HMF formation.

Understanding the nature of NH3-coordinated active sites and the complete reaction schemes for NH3-SCR using Cu-SAPO-34 catalysts.

Cu-SAPO-34 zeolite catalysts show excellent NH3-SCR performance at low temperature, which is due to the catalytic capacity of copper species. Isolated CuII ions and CuIIOH are active sites, but their nature and role are not fully understood. This paper reports the DFT calculations in combination with ab initio thermodynamics to investigate NH3 and H2O coordination to copper species under typical NH3-SCR reaction conditions. In the reduction part of the NH3-SCR reaction, NH2NO and NH4NO2 intermediates will form on CuII-2NH3/3NH3 and CuIIOH-2NH3 complexes, respectively. The Brønsted acid sites are crucial for the decomposition of these intermediates, rather than copper species. Furthermore, the decomposition of NH2NO is more energetically favorable than NH4NO2 which are formed on the Brønsted acid sites. In the re-oxidation part of the NH3-SCR reaction, O2 dissociation and NO2 formation occur on CuI-2NH3 complexes in the presence of NO, and the regeneration of CuIIOH-2NH3 requires the participation of H2O. The proposed complete mechanisms highlight the importance of ligand coordinated copper species for intermediate formation and O2 activation in NH3-SCR.

Irregular influence of alkali metals on Cu-SAPO-34 catalyst for selective catalytic reduction of NOx with ammonia.

SCR activity of Cu-SAPO-34 catalyst was reduced by alkali metal ions. The alkali metals ions (Li+, Na+ and K+) have shown irregular influences on Cu-SAPO-34. The order of poisoning strengths under 400 °C was found to be: Na+ > K+ > Li+, which is not consistent with the basicities of their corresponding metals. Experimental results and calculations showed that the alkali metal ions readily replace H+ and Cu2+/Cu+ ions. These exchanges result in the loss of Brønsted acid sites and migration of isolated Cu2+ ions in Cu-SAPO-34, which decrease the NH3-SCR activity. Both the basicity and ion diameter will affect the exchanging behavior of an alkali ion. Na+ and Li+ ions will influence both H+ and Cu2+/Cu+ ions but K+ ions only preferably replace the H+. We hypothesize that K+ cannot enter into a small ring (6-membered ring) to replace a Cu2+/Cu+ ion because of its large ion diameter. The displaced Cu2+/Cu+ ions will transfer to adjacent unbonded Al site to form a CuAlO2 species.

Promoting effects of water on the NH3-SCR reaction over Cu-SAPO-34 catalysts: transient and permanent influences on Cu species.

Cu-SAPO-34 catalysts with varied Cu loadings were synthesized through ion exchange to study the influence of water on the NH3-SCR reaction. The catalytic activities were evaluated by selective catalytic reduction of NO under a reactant feed in the presence/absence of water. Transient experiments were designed to study the response of NO conversion to the presence of water. H2-TPR and DFT calculations were performed to study the reducibility of Cu species. NH3-TPD and XPS were conducted to reveal the migration of Cu species. The results show that water could remarkably improve NO reduction activities and the promoting effect is more significant on the catalyst with low Cu loading. Both transient and permanent influences were found in this promoting phenomenon. For the transient influence, water has been proved to accelerate the re-oxidation half-cycle. Moreover, water can enhance the promoting effect of the SCR feed on the migration of Cu species. These unanchored Cu ions migrate to defect sites to form active sites, which lead to a permanent influence of water.

[Analysis and computational fluid dynamics simulation of hemodynamic influences caused by splenic vein thrombosis].

This paper aims to analyze the impact of splenic vein thrombosis (SVT) on the hemodynamic parameters in hepatic portal vein system. Based on computed tomography (CT) images of a patient with portal hypertension and commercial software MIMICS, the patient's portal venous system model was reconstructed. Color Doppler ultrasound method was used to measure the blood flow velocity in portal vein system and then the blood flow velocities were used as the inlet boundary conditions of simulation. By using the computational fluid dynamics (CFD) method, we simulated the changes of hemodynamic parameters in portal venous system with and without splenic vein thrombosis and analyzed the influence of physiological processes. The simulation results reproduced the blood flow process in portal venous system and the results showed that the splenic vein thrombosis caused serious impacts on hemodynamics. When blood flowed through the thrombosis, blood pressure reduced, flow velocity and wall shear stress increased. Flow resistance increased, blood flow velocity slowed down, the pressure gradient and wall shear stress distribution were more uniform in portal vein. The blood supply to liver decreased. Splenic vein thrombosis led to the possibility of forming new thrombosis in portal vein and surroundings.

The co-effect of Sb and Nb on the SCR performance of the V2O5/TiO2 catalyst.

The effect of the Sb and Nb additives on the V(2)O(5)/TiO(2) catalyst for the selective catalytic reduction (SCR) of NO with NH(3) was investigated. The experimental results show that either Nb or Sb can improve the activity of V(2)O(5)/TiO(2) catalyst. Higher Nb loading led to higher N(2) selectivity. The co-doping of Sb and Nb showed higher improving effect than the single doping of Sb or Nb. The V(2)O(5)/TiO(2) catalyst doped with Sb and Nb had a better H(2)O resistance than the V(2)O(5)/TiO(2) catalyst. The addition of Sb and Nb also enhance the resistance of the V(2)O(5)/TiO(2) catalyst to K(2)O poisoning. The catalysts were characterized by BET, XRD, TEM, and XPS. The results showed that the active components of V, Sb, and Nb were well interacting with each other. The coexistence of Sb and Nb will enhance the redox ability and surface acidity and thus promote the SCR performance.