Na Cocations and Hydrothermal Aging Cooperatively Boost the Regeneration of Phosphorus-Poisoned Pd/SSZ-13 for Passive NOx Adsorption.

Pd/SSZ-13 has been proposed as a passive NOx adsorber (PNA) for low-temperature NOx adsorption. However, it remains challenging for Pd/SSZ-13 to work efficiently when suffering from phosphorus poisoning. Herein, we report a simple and efficient strategy to regenerate the phosphorus-poisoned Pd/SSZ-13 based on the cooperation between hydrothermal aging treatment and Na cocations. It was found that hydrothermal aging treatment enabled the redispersion of Pd and P-containing species in phosphorus-poisoned Pd/SSZ-13. Meanwhile, the presence of Na cocations significantly reduced the formation of AlPO4 and retained more paired Al sites for highly dispersed Pd2+ ions, which was of great importance for the recovery of adsorption performance. To our satisfaction, the restoration ratio of the adsorption capacity of poisoned Pd/SSZ-13 was >90% after regeneration. Strikingly, the NOx adsorption activities of phosphorus-poisoned Pd/SSZ-13 with phosphorus loadings of 0.2 and 0.4 mmol g-1 almost completely recovered upon regeneration. This study demonstrates the promoting effect of Na cocations on the regeneration of phosphorus-poisoned Pd/SSZ-13 by hydrothermal aging treatment, which provides useful guidance for the design of PNA materials with excellent durability for cold-start application.

Coaxial 3D Printing of Zeolite-Based Core-Shell Monolithic Cu-SSZ-13@SiO2 Catalysts for Diesel Exhaust Treatment.

Core-shell catalysts with functional shells can increase the activity and stability of the catalysts in selective catalytic reduction of NOx with ammoniax . However, the conventional approaches based on multistep fabrication for core-shell structures encounter persistent restrictions regarding strict synthesis conditions and limited design flexibility. Herein, a facile coaxial 3D printing strategy is for the first time developed to construct zeolite-based core-shell monolithic catalysts with interconnected honeycomb structures, in which the hydrophilic noncompact silica serves as shell and Cu-SSZ-13 zeolite acts as core. Compared to a Cu-SSZ-13 monolith which suffers from the interfacial diffusion, the SiO2 shell layer can increase the accessibility of active sites over Cu-SSZ-13@SiO2 , resulting in a 10-20% higher NO conversion at200-550 °C under 300 000 cm3 g-1 h-1 . Meanwhile, a thicker SiO2 shell enhances the hydrothermal stability of the aged catalyst by inhibiting the dealumination and the formation of CuOx . Other representative monolithic catalysts with different topological zeolites as shell and diverse metal oxides as the core can be also realized by this coaxial 3D printing. This strategy allows multiple porous materials to be directly integrated, which allows for flexible design and fabrication of various core-shell monolithic catalysts with customized functionalities.

Unraveling templated-regulated distribution of isolated SiO4 tetrahedra in silicoaluminophosphate zeolites with high-throughput computations.

Silicoaluminophosphate (SAPO) zeolites are well-known catalytic materials because of the mild acidity originating from the isolated SiO4 tetrahedra in their frameworks. Regulating the distribution of isolated SiO4 tetrahedra in SAPO zeolites is formidably challenging because SiO4 tetrahedra tend to agglomerate to form Si islands and the isolated SiO4 tetrahedra are difficult to determine using conventional characterization techniques. Here we synthesized Si-island-free SAPO-35 zeolites by using N-methylpiperidine as a new template, which exhibited excellent thermal stability compared to conventional SAPO-35 zeolites and a substantially improved methanol-to-olefins catalytic lifetime even comparable to that of commercial SAPO-34 zeolites. More strikingly, with the aid of high-throughput computations on 44 697 structure models combined with various state-of-the-art characterization techniques, for the first time, we reveal that the host-guest interactions between template molecules and SAPO frameworks determine the specific distributions of isolated SiO4 tetrahedra, which are responsible for the improvement in the chemical properties of zeolites. Our work provides an insight into the template-based regulation of isolated SiO4 tetrahedra in SAPO zeolites, which opens a new avenue in the discovery of promising zeolite catalysts with optimal SiO4 distribution.

Seed-Assisted Synthesis of Hierarchically Structured Nano-Sized Ti-ß Zeolites for the Efficient Epoxidation Reaction of Alkenes.

The development of nano-sized titanosilicate zeolites with hierarchical structures is crucial in promoting the efficient epoxidation of alkenes. In the present work, nano-sized hierarchical Ti-ß (*BEA) zeolites with high crystal yield are prepared by a one-pot nanoseed-assisted approach. The influence of seed size on the resultant Ti-ß zeolites is investigated by complementary characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, UV-vis diffuse reflectance spectroscopy (DRS), and UV Raman spectroscopy. The possible process for the formation of hierarchical Ti-ß nanocrystals with the assistance of nanoseeds in the synthesis gel is proposed. Consequentially, the nano-sized hierarchical material prepared by the nanoseed-assisted method shows excellent mass transportation and accessibility to active sites by reducing particle size and constructing hierarchical porosity, hence showing a remarkably enhanced catalytic activity and selectivity in the epoxidation reaction of alkenes. This work will shed light on the efficient preparation of nano-sized titanosilicate zeolites.

Amino Acid-Assisted Construction of Single-Crystalline Hierarchical Nanozeolites via Oriented-Aggregation and Intraparticle Ripening.

Hierarchical nanozeolites are highly desired for heavy oil conversion because of their fast mass transfer, good site accessibility, and short diffusion length compared with their conventional counterparts. Here, we provide a facile amino acid-assisted strategy to synthesize hierarchical ZSM-5 (MFI) zeolite nanocrystals by two-step crystallization in a concentrated gel system. Strikingly, each virus-like zeolite nanoparticle with abundant interconnected intracrystalline mesopores is a high-quality single crystal that is defect-free as confirmed by electron diffraction and NMR analysis. By utilizing advanced electron microscopy techniques, we have studied the evolution process of single-crystalline hierarchical ZSM-5 nanocrystals that involves oriented aggregation of protozeolitic nanoparticles formed at low temperature followed by intraparticle ripening at high temperature. The as-prepared hierarchical Ni@ZSM-5 catalysts exhibit superior catalytic performance in hydrodeoxygenation of stearic acid and palm oil.

The Nature of Hydrogen Adsorption on Platinum in the Aqueous Phase.

The thermodynamic state of H2 adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H2 reacting with D2 O to HDO, HD, and D2 , and by DFT-based ab initio molecular dynamics simulations of H2 adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H2 on Pt is significantly weakened in the aqueous phase compared to adsorption at gas-solid interfaces. Water destabilizes the adsorbed H atoms, decreasing the heat of adsorption by 19-22 kJ m o l H 2 - 1 while inducing an additional entropy loss of 50-70 J m o l H 2 - 1 K-1 . Upon dissociative adsorption of H2 , the average distance of water from the Pt surface increases and the liquid adopts a structure that is more ordered than before close to the Pt surface, which limits the translation mobility of the adsorbed H atoms. The presence of hydrated hydronium ions next to the Pt surface further lowers the H-Pt bond strength.

H-Transfer reactions of internal alkenes with tertiary amines as H-donors on carbon supported noble metals.

A hydride transfer reaction with tertiary amines was observed in the presence of noble metals on a carbon support. Hydride transfer had been documented previously in terms of activated allyl-type carbon-carbon double bonds containing carbonyl derivatives in the presence of triethyl amine (conjugate reduction). The proposed mechanism is a hydride transfer reaction in which the metal serves as the reaction partner of the hydrido-metal iminium adduct formation. The saturation of a non-activated internal double bond containing compound, such as methyl oleate and trans-5-decene as substrates, was observed for the first time in this work. The pre-reduced catalyst samples showed high activity; in the presence of Pd/C, Pt/C and Rh/C partial to complete conversion was detected at 140 °C in a p-xylene solvent without molecular hydrogen. Higher molecular weight byproducts of the amines were formed, while in the case of the substrates negligible amounts of unreacted but double bond migrated species were present. There is a possibility of usage of alkyl amines other than triethylamine; thus use of tributyl-, tripentyl-, trihexylamine and N,N-diisopropylethylamine, as well as cyclic 1-ethylpyrrolidine and 1-ethylpiperidine, was investigated. Cyclic amines and diisopropyl derivatives as H sources produced the highest conversion, while amines with longer alkyl chains showed minor activity. As a clear indication of H-donation, the formation of unsaturated amine species such as 1-ethyl-pyrrole and pyridine was observed.