Effects of Next-Nearest-Neighbor Aluminum Location on the Brønsted Acidity of HY Zeolites

The distribution of aluminum (Al) on the H-form zeolite framework strongly affects the Brønsted acidity, resulting in the corresponding acid-catalyzed reactivity of zeolite catalysts. In the present work, the effects of next-nearest-neighbor (NNN) Al locations and numbers on the acidity for the specific Brønsted acid sites (BAS) inside the channel and on the external surface of the HY zeolites with two Si/Al ratios were investigated using density functional theory calculations. The Gibbs free energy of ammonia adsorption at the BAS site with different local NNN Al environments was used to characterize the Brønsted acidity. It has been found that an NNN Al atom on the β cage slightly enhances the acidity, while NNN Al atoms at the hexagonal column and super cages significantly decrease the acidity. With the increasing number of NNN Al atoms, the acidity of the specific BAS becomes weaker. The effects of the NNN Al location and numbers on the Brønsted acidity are further confirmed using pyridine, indole, and quinoline as probe molecules

One-Pot Synthesis of Mesoporous Silica Nanocarriers with Tunable Particle Sizes and Pendent Carboxylic Groups for Cisplatin Delivery

Mesoporous silica nanocarriers with tunable particle sizes and different loadings of pendent carboxylic groups were successfully prepared by a straightforward and reproducible strategy, in which carboxyethylsilanetriol sodium salt was co-condensed with tetraethoxyorthosilicate to introduce the carboxylic groups. The key in this strategy was to separate the synthesis process into two steps of the nuclei formation and particle growth. The uniform particle size and ordered structure of the synthesized nanocarriers were manifested by several techniques such as XRD, TEM, SEM, and BET. DLS measurement illustrated that nanocarriers could be well suspended in aqueous solution. The integration and content tunability of the carboxylic groups within mesoporous silica nanoparticles (MSNs) were verified by FT-IR and ²⁹Si NMR. The inherent carboxylic units on the obtained carboxylic group modified MSNs (MSNs-C) effectively enhanced the capture and tailored the release properties of the anticancer drug of cisplatin. The accumulation of drug in the HeLa cells was greatly enhanced due to the highly efficient platinum uptake efficiency transported by the synthesized nanocarriers. The drug encapsulated in the MSNs-C exhibited a higher antitumor activity than free cisplatin against both MCF-7 and HeLa cells

Synthesis of gold Nanoshells through Improved Seed-Mediated Growth Approach: Brust-like, <i>in Situ</i> Seed Formation

Gold nanoshells have shown great potentials in various fields. However, the widely used seed-mediated growth method based on a silica template for gold nanoshells is a complex and time-consuming procedure. In this work, mercaptosilica was first used as a template to synthesize gold nanoshells through improved seed-mediated growth method. It is verified that gold seeds were formed and attached onto the mercaptosilica nanospheres through Brust-like, <i>in situ</i> process, which makes this method extremely time-saving and easy to manipulate. Importantly, the key factors affecting the <i>in situ</i> process were demonstrated, allowing fine control on the synthesis in a highly reproducible manner. The as-synthesized nanoshells are monodisperse with well-defined morphology and tunable near-IR plasmon resonance. Furthermore, other metal nanoparticles such as Pt and Pd could be grafted onto the surface of mercaptosilica nanospheres through the same Brust-like, <i>in situ</i> process. These provide new insights into seed attachment, and the improved seed-mediated growth approach based on Brust-like, <i>in situ</i> seed formation will take an important step forward toward the widespread application of gold nanoshells

Fabrication of Hierarchically Porous RuO₂–CuO/Al–ZrO₂ Composite as Highly Efficient Catalyst for Ammonia-Selective Catalytic Oxidation

A hierarchically porous RuO₂–CuO/(Al–ZrO₂) nanocomposite, with RuO₂ and CuO nanocrystals being homogeneously dispersed in the hierarchically porous structure of Al-doped ZrO₂ (Al–ZrO₂), has been developed by a hydrothermal and wet impregnation method for efficient ammonia-selective catalytic oxidation (SCO) applications. The microstructures of the RuO₂–CuO/Al–ZrO₂ nanocomposites were characterized by XRD, TEM, FESEM, EDX elemental mapping, and N₂ sorption. XPS analysis and H₂-TPR results indicate that the hierarchically porous RuO₂–CuO/Al–ZrO₂ composites possess a large number of oxygen vacancies and surface catalytic active sites, which endows the composite with high catalytic activity and N₂ selectivity for NH₃ oxidation. NH₃ complete oxidization has been achieved at 195 °C with 100% N₂ selectivity over an obtained RuO₂–CuO/Al–ZrO₂ composite at RuO/CuO = 1:1 (weight rate). The high efficiency of hierarchically porous RuO₂–CuO/Al–ZrO₂ nanocomposites for ammonia SCO reaction has been attributed to the synergetic catalytic effects among the metal oxides, in which the porous Al–ZrO₂ support promotes oxygen activation by the generation of oxygen vacancies due to the Al doping, and the ultrahigh catalytic activity of RuO₂ is responsible for the active NH₃ oxidation. Successively, CuO plays a role of NO intermediate conversion for enhanced N₂ selectivity

Effective Adsorption and Enhanced Removal of Organophosphorus Pesticides from Aqueous Solution by Zr-Based MOFs of UiO-67

Though many efforts have been devoted to the adsorptive removal of hazardous materials of organophosphorus pesticides (OPs), it is still highly desirable to develop novel adsorbents with high adsorption capacities. In the current work, the removal of two representative OPs, glyphosate (GP) and glufosinate (GF), was investigated by the exceptionally stable Zr-based MOFs of UiO-67. The abundant Zr–OH groups, resulting from the missing-linker induced terminal hydroxyl groups and the inherent bridging ones in Zr–O clusters of UiO-67 particles, served as natural anchorages for efficient GP and GF capture in relation with their high affinity toward phosphoric groups in OPs. The correlation between the most significant parameters such as contact time, OPs concentration, adsorbent dose, pH, as well as ionic strength with the adsorption capacities was optimized, and the effects of these parameters on the removal efficiency of GP and GF from the polluted aqueous solution were investigated. The adsorption of GP on UiO-67 was faster than that of GF, and a pseudo-second-order rate equation effectively described the uptake kinetics. The Langmuir model exhibited a better fit to adsorption isotherm than the Freundlich model. Thanks to the strong affinity and adequate pore size, the adsorption capacities in UiO-67 approached as high as 3.18 mmol (537 mg) g^–1 for GP and 1.98 mmol (360 mg) g^–1 for GF, which were much higher than those of many other reported adsorbents. The excellent adsorption characteristics of the current adsorbents toward OPs were preserved in a wide pH window and high concentration of the background electrolytes. These prefigured the promising potentials of UiO-67 as novel adsorbent for the efficient removal of OPs from aqueous solution

Methane–H₂S Reforming Catalyzed by Carbon and Metal Sulfide Stabilized Sulfur Dimers

H2S reforming of methane (HRM) provides a potential strategy to directly utilize sour natural gas for the production of COx-free H2 and sulfur chemicals. Several carbon allotropes were found to be active and selective for HRM, while the additional presence of transition metals led to further rate enhancements and outstanding stability (e.g., Ru supported on carbon black). Most metals are transformed to sulfides, but the carbon supports prevent sintering under the harsh reaction conditions. Supported by theoretical calculations, kinetic and isotopic investigations with representative catalysts showed that H2S decomposition and the recombination of surface H atoms are quasi-equilibrated, while the first C–H bond scission is the kinetically relevant step. Theory and experiments jointly establish that dynamically formed surface sulfur dimers are responsible for methane activation and catalytic turnovers on sulfide and carbon surfaces that are otherwise inert without reaction-derived active sites

Cu-OFF/ERI Zeolite: Intergrowth Structure Synergistically Boosting Selective Catalytic Reduction of NO_<i>x</i> with NH₃

Cu-SSZ-13 has been commercialized for selective catalytic reduction with ammonia (NH3–SCR) to remove NOx from diesel exhaust. As its synthesis usually requires toxic and costly organic templates, the discovery of alternative Cu-based zeolite catalysts with organotemplate-free synthesis and comparable or even superior NH3–SCR activity to that of Cu-SSZ-13 is of great academic and industrial significance. Herein, we demonstrated that Cu-T with an intergrowth structure of offretite (OFF) and erionite (ERI) synthesized by an organotemplate-free method showed better catalytic performance than Cu-ERI and Cu-OFF as well as Cu-SSZ-13. Structure characterizations and density functional theory calculations indicated that the intergrowth structure promoted more isolated Cu2+ located at the 6MR of the intergrowth interface, resulting in a better hydrothermal stability of Cu-T than Cu-ERI and Cu-OFF. Strikingly, the low-temperature activity of Cu-T significantly increased after hydrothermal aging, while that of Cu-ERI and Cu-OFF substantially decreased. Based on in situ diffuse reflectance infrared Fourier transform spectra analysis and density functional theory calculations, the reason can be attributed to the fact that NH4NO3 formed on the CuxOy species within ERI polymorph of Cu-T underwent a fast SCR reaction pathway with the assistance of Brønsted acid sites at the intergrowth interfaces under standard SCR reaction conditions. Significantly, Cu-T exhibited a wider temperature window at a catalytic activity of over 90% than Cu-SSZ-13 (175–550 vs 175–500 °C for fresh and 225–500 vs 250–400 °C for hydrothermal treatment). This work provides a new direction for the design of high-performance NH3–SCR catalysts in terms of the interplay of the intergrowth structure of zeolites