Search

• Pd@Beta and Pd@MOR with encapsulation structure can be prepared by seeding method. • Pd@Beta and Pd@MOR can obtain higher Pd dispersion and aggregation resistance. • The encapsulated bifunctional catalysts exhibit higher isomerization selectivity. • Zeolite topology and size may affect the intimacy of the encapsulated catalysts. The bifunctional catalysts capable of regulating the metal dispersion and location through encapsulating palladium (Pd) nanoparticles inside Beta and mordenite (MOR) zeolites were used for n-heptane hydroisomerization. Several characterizations such as X-ray powder diffraction (XRD), scanning electron microscope (SEM), N 2 -adsorption and so on suggested that the difference in the phase, textural property, morphology, and acidity of zeolites between the catalysts with encapsulation structure and prepared by impregnation method was negligible whether Beta- or MOR-series catalysts. Nevertheless, the higher Pd dispersion, smaller Pd particle size, and higher aggregation resistance can be achieved on the encapsulation catalysts as determined by H 2 -pulse and transmission electron microscopy (TEM). Compared to the palladium-loading catalyst prepared by conventional impregnation method, the encapsulation structure guaranteed the higher selectivity and yield in n-heptane isomerization due to the significantly improved balance and intimacy. Furthermore, the catalyst with the complete encapsulation structure for the Beta-series catalysts and the catalyst with partial encapsulation structure for the MOR-series catalysts respectively exhibited the highest isomer selectivity and yield. All results may be resulted from that the zeolite topology and crystal size acted a significant role in determining the intimacy of the bifunctional catalysts with encapsulation structure, due to the different diffusion hurdles of the channels structure. [ABSTRACT FROM AUTHOR]

• High C/N ratios and effluent recirculation promoted SND process for N removal. • HNAD was the main nitrogen transformation pathway in TFCWs. • HNADB were the dominant functional genera related to nitrogen removal in TFCWs. • Some core HNADB showed positive interactions with other functional genera. • Tidal strategies contributed more to shifts in functional genera than C/N ratios. This study investigated the influence of C/N ratios and tidal strategies on nitrogen removal and bacterial communities in two pilot-scale tidal flow constructed wetlands (TFCWs) with simultaneous nitrification–denitrification process. Heterotrophic nitrification aerobic denitrification (HNAD) was the main nitrogen transformation pathway in both TFCWs. High C/N ratios and effluent circulation at low temperature promoted HNAD in TFCWs with high nitrogen removal efficiencies (72.6%–95.5% for NH 4 +-N and 70.9%~91.8% for TN). Effluent circulation had more influence on bacterial community structure and diversity than C/N ratios. Among 16 detected genera related to nitrogen removal, HNAD bacteria (HNADB) were abundant. Especially, some dominant HNADB (e.g. Aeromonas , Hydrogenophage and Gemmobacter) were core genera, showing positive interactions with other genera related to nitrogen removal. Tidal strategies had more contribution to the shifts in these genera than C/N ratios. This study highlights the importance of HNADB in pilot-scale TFCWs and their responses to C/N ratios and tidal strategies. [ABSTRACT FROM AUTHOR]

• Coverage dependent hydrogen adsorption on Ir(111), Ir(100) and Ir(110) surfaces. • Change of adsorption site on Ir(100) from low to high coverage. • Surface dependent repulsive interaction on Ir(111). • Surface dependent attractive interaction on Ir(100) and Ir(110). • Regular line-shaped adsorption structures were found on Ir(100) and Ir(110). Hydrogen adsorption on the perfect Ir(111) as well as the metastable and unreconstructed Ir(100) and Ir(110) surfaces up to saturation coverage has been systematically computed using periodic density functional theory and ab initio atomistic thermodynamics for understanding the interaction mechanism of hydrogen on iridium surfaces. On the Ir(111) surface including van der Waals dispersion, hydrogen adsorption prefers the threefold hollow sites at low coverage and the top sites at high coverage; in agreement with the experiments (Phys. Rev. B 60 (1999) 14016). The computed adsorption energy and desorption temperature of hydrogen agree with the experiments [−0.57 (fcc-3H) and −0.53 (hcp-3H) vs. −0.55 eV; 180 and 325 K vs. 190 and 310 K, respectively]. On the Ir (100) surface, the bridge adsorption sites are preferred in the whole coverage range, in agreement with the LEED pattern (Phys. Rev. B 73 (2006) 75430), however, adsorption energy and desorption temperature are slightly overestimated by including van der Waals dispersion (−1.50 vs. −1.02 ± 0.15 eV; 470 vs. 425 – 389 K). On the Ir(110) surface, short-bridge sites are preferred at low coverage and the top sites become dominant at high coverage, and the calculated desorption temperatures are close to experiments by including van der Waals dispersion (210 and 365 K vs. 220 and 375 K). At low coverage, the different configurations of hydrogen adsorption on the Ir(111) have the similar energies, indicating their negligible repulsive interaction, while the Ir(100) and Ir(110) surfaces prefer regular line-shape adsorption configurations due to attractive interaction, and such adsorption configurations have not been observed experimentally. Our results show that differences in adsorption configurations and energies are associated with their differences in surface structures, and in turn explain the need of different methods in computing the adsorption properties on different surfaces. Such surface-dependent properties should also be possible on other metal surfaces. Image, graphical abstract [ABSTRACT FROM AUTHOR]