Revealing the BroÌ·nsted Acidic Nature of Penta-Coordinated Aluminum Species in Dealuminated Zeolite Y with Solid-State NMR Spectroscopy.

The inevitable dealumination process of zeolite Y is closely related to ultrastabilization, enhanced BroÌ·nsted acidity, and deactivation throughout its life cycle, producing complex aluminum and acidic hydroxyl species. Most investigations on dehydrated zeolites have focused on the BroÌ·nsted acidity of tetra-coordinated Al (Al(IV)) and Lewis acidity associated with tricoordinated Al (Al(III)) sites, which has left the penta-coordinated Al (Al(V)) in dealuminated zeolites scarcely discussed. This is largely due to the oversimplified view of detectable Al(V) as an exclusively extra-framework species with Lewis acidity. Here we report the formation of BroÌ·nsted acidic penta-coordinated Al species (Al(V)-BAS) in the dealumination process. Two-dimensional (2D) through-bond and multiquantum 1H-{27Al} correlation solid-state NMR experiments demonstrate the presence of a bridging Si-OH-Al(V) structure in dealuminated Y zeolites. Different from the conventional belief that water attack leads to the breaking of zeolite framework Al-O bonds in the initial stage of zeolite dealumination, the observed Al(V) as a dealumination intermediate is directly correlated with a BAS pair because of the direct dissociation of water on the framework tetrahedral aluminum (Al(IV)), thus bypassing the cleavage of Al-O bonds. 1H double-quantum solid-state NMR experiments and theoretical calculations provide further evidence for this mechanism, whereas pyridine adsorption experiments confirm stronger acidity of Al(V)-BASs than the traditional bridging hydroxyl groups associated with Al(IV). We were also able to detect the Al(V)-BAS site from dealuminated SSZ-13 zeolite with CHA topology, suggesting that its creation is not specific to the framework structure of zeolites.

Hydrothermal Aging Enhances Nitrogen Oxide Reduction over Iron-Exchanged Zeolites at 150 °C.

Ammonia selective catalytic reduction (NH3-SCR) over copper- and iron-exchanged zeolites is a state-of-the-art technology for removal of nitrogen oxides (NOx, NO, and NO2) from exhaust emissions but suffers from poor low-temperature (i.e., 150 °C) activity. Here we show that hydrothermal aging of Fe-beta, Fe-ZSM-5, and Fe-ferrierite at 650 °C or higher leads to a remarkable increase in NOx conversion from ∼30 to ∼80% under fast NH3-SCR conditions at 150 °C. The practical relevance of this finding becomes more evident as an aged Fe-beta/fresh Cu-SSZ-13 composite catalyst exhibits ∼90% conversion. We propose that a neutral heteronuclear bis-µ-oxo ironaluminum dimer might be created within iron zeolites during hydrothermal aging and catalyze ammonium nitrate reduction by NO at 150 °C. Density functional theory calculations reveal that the activation free energy (125 versus 147 kJ mol-1) for the reaction of NO with adsorbed NO3- species, the rate-determining step of ammonium nitrate reduction, is considerably lower on the bis-µ-oxo ironaluminum site than on the well-known mononuclear iron-oxo cation site, thus greatly enhancing the overall SCR activity.

The deactivation of a ZnO doped ZrO2-SiO2 catalyst in the conversion of ethanol/acetaldehyde to 1,3-butadiene.

A deactivation study on the ethanol/acetaldehyde conversion to 1,3-butadiene over a ZnO promoted ZrO2-SiO2 catalyst prepared by a sol-gel method was performed. The samples were characterized by N2 adsorption-desorption isotherms, scanning electron microscopy (SEM), NH3 temperature programmed desorption (NH3-TPD), X-ray powder diffraction characterization (XRD), thermogravimetric analyses (TGA), Fourier transform infrared resonance (FT-IR), 13C magic-angle spinning nuclear magnetic resonance (13C NMR) and X-ray photoelectron spectroscopy (XPS). The pore structure characteristics and surface acidity of Zn0.5-Zr-Si catalysts were largely decreased with time-on-stream and no crystal structure was formed in the used catalyst, indicating that the deactivation was caused by carbon deposition. Two main types of carbon deposition were formed, namely low-temperature carbon deposition with the oxidation temperature of around 400 °C and high-temperature carbon deposition with the oxidation temperature of 526 °C. The carbon species were mainly composed of graphitized carbon, amorphous carbon, carbon in C-O bonds and carbonyls. The deactivated catalyst could be regenerated by a simple oxidation process in air. Adding a certain amount of water into the feed had a positive effect on reducing the carbon deposition.

Molecular chaperone Jiv promotes the RNA replication of classical swine fever virus.

The nonstructural protein 2 (NS2) of classical swine fever virus (CSFV) is a self-splicing ribozyme wherein the precursor protein NS2-3 is cleaved, and the cleavage efficiency of NS2-3 is crucial to the replication of viral RNA. However, the proteolytic activity of NS2 autoprotease may be achieved through a cellular chaperone called J-domain protein interacting with viral protein (Jiv) or its fragment Jiv90, as evidence suggests that Jiv is required for the proper functioning of the NS2 protein of bovine viral diarrhea virus. Hence, the expression of Jiv may be correlated with the replication efficiency of CSFV RNA. We investigated the expression levels of Jiv and viral RNA in CSFV-infected cells and tissues using Real-time RT-PCR or Western blot analysis. The obtained results show that Jiv90 possibly plays an important role in the lifecycle of CSFV because the distribution of Jiv90 protein shows a positive correlation with the viral load of CSFV. Furthermore, the overexpression or knockdown of Jiv90 in swine cells can also significantly promote or decrease the viral load, respectively. The detection of Flow cytometry shows that the overexpression of Jiv90 prolongs the G1 phase of cell cycles but has no effect on apoptosis. These findings are likely to be of benefit in clarifying the pathogenesis of the CSFV.

Detection and differentiation of classical swine fever virus strains C and Shimen by high-resolution melt analysis.

Differentiation of classical swine fever virus (CSFV) strains is crucial for the development of effective vaccination programs and in epidemiological investigations. Most of current detection methods do not discriminate between wild-type CSFV strains and those used in vaccines. In this study, method involving high-resolution melt (HRM) curve analysis for the simultaneous detection and differentiation of the C and Shimen strains of CSFV was developed. A specific fragment of the NS2 gene was amplified from various CSFV strains and subjected to HRM curve analysis. Analysis of the melt curve profile for the amplicons of each strain allowed the differentiation of CSFV strains in blood samples taken from the field, or from vaccinated commercial flocks. These findings indicate that HRM curve analysis is a rapid and practical technique for discriminating CSFV isolates/strains; it can contribute to epidemiological studies of CSFV and effective control of classical swine fever.