A new insight into the theoretical design of highly dispersed and stable ceria supported metal nanoparticles

Insights into Adsorption Behavior and Mechanism of Br- onto Nickel-Aluminum Layered Double Hydroxides Intercalated with Different Inorganic Anions

Layered double hydroxides (LDHs) have garnered significant attention from researchers in the field of adsorption due to their unique laminated structures and ion exchange properties. LDHs with various anion intercalation showed different adsorption effects on adsorbing ions, but the corresponding adsorption mechanisms are ambiguous. In this study, three types of NiAl-LDHs were synthesized, utilizing NO3-, CO32-, or Cl- as the interlayer anions. Batch tests were conducted to study their adsorption performances for Br-. Among them, the LDH with a NO3- intercalation layer exhibited the highest adsorption capacity for Br-, reaching up to 1.40 mmol g-1. The adsorption kinetics, mechanism, and renewability of these NiAl-LDHs were systematically compared. As a result, the type of Br- adsorption by all three materials was single molecular layer chemisorption. Moreover, the thermodynamic results of adsorption suggested that the adsorption of Br- was a spontaneous exothermic process. X-ray photoelectron spectroscopy, X-ray diffraction, and point of zero charge analysis collectively indicated that the adsorption of Br- by LDHs primarily occurred through interlayer ion exchange and electrostatic interactions. Structural characterizations of the adsorbents revealed that Br- entered the interlayers of the three LDHs, causing varying degrees of reduction in the interlayer spacing. Density functional theory calculations indicated that the interlayer binding energy of LDH with NO3- intercalation was the lowest, thereby making it more susceptible NO3- to be exchanged with Br-. Finally, the stability of the NiAl-LDHs was studied. The NiAl-LDHs retains a high removal efficiency of Br- even after 5 cycles of adsorption and desorption.

Selective, rapid extraction of uranium from aqueous solution by porous chitosan-phosphorylated chitosan-amidoxime macroporous resin composite and differential charge calculation

Herein, a new porous chitosan-phosphorylated chitosan-amidoxime macroporous resin composite (PCAR) was designed and synthesized for the rapid and selective extraction of uranium resources from aqueous solution. This study showed that PCAR exhibited excellent adsorption toward uranium in a pH range of 5-9. The dynamic adsorption process aligned with the quasi-second-order kinetic model and corresponded to the chemical adsorption process. The maximum adsorption capacity was 561.28 mg·g-1 at pH 6 and 308 K. Mechanism analysis showed that the synergistic effect of the amidoxime group (-(NH2)C=N-OH), PO, and -NH2 on the PCAR surface improved the uranium adsorption performance. The differential charge density indicated that the amidoxime and phosphate groups provide lone-pair electrons for the adsorption of UO22+ and their synergistic effect improves the UO22+ adsorption performance of PCAR. The uranium distribution coefficients of PCAR and CAR are 4.6 and 2.4 times those of vanadium, respectively. These results indicate that phosphorylation can ameliorate the disadvantage of competitive vanadium adsorption of the amidoxime adsorbent. In addition, PCAR exhibits good reusability and stable adsorption capacity after five adsorption-desorption cycles. Hence, PCAR has excellent potential for uranium extraction from aqueous solution.

Recent Advances in Design of Gold-Based Catalysts for H2 Clean-Up Reactions

Over the past three decades, supported gold nanoparticles have demonstrated outstanding properties and continue to attract the interest of the scientific community. Several books and comprehensive reviews as well as numerous papers cover a variety of fundamental and applied aspects specific to gold-based catalyst synthesis, characterization by different techniques, relationship among catalyst support features, electronic and structural properties of gold particles, and catalytic activity, reaction mechanism, and theoretical modeling. Among the Au-catalyzed reactions targeting environmental protection and sustainable energy applications, particular attention is paid to pure hydrogen production. The increasing demands for high-purity hydrogen for fuel cell systems caused a renewed interest in the water-gas shift reaction. This well-known industrial process provides an attractive way for hydrogen generation and additional increase of its concentration in the gas mixtures obtained by processes utilizing coal, petroleum, or biomass resources. An effective step for further elimination of CO traces from the reformate stream after water-gas shift unit is the preferential CO oxidation. Developing highly active, stable, and selective catalysts for these two reactions is of primary importance for efficient upgrading of hydrogen purity in fuel cell applications. This review aims to extend the existing knowledge and understanding of the properties of gold-based catalysts for H2 clean-up reactions. In particular, new approaches and strategies for design of high-performing and cost-effective formulations are addressed. Emphasis is placed on efforts to explore appropriate and economically viable supports with complex composition prepared by various synthesis procedures. Relevance of ceria application as a support for new-generation WGS catalysts is pointed out. The role of the nature of support in catalyst behavior and specifically the existence of an active gold-support interface is highlighted. Long-term stability and tolerance toward start-up/shutdown cycling are discussed. Very recent advances in catalyst design are described focusing on structured catalysts and microchannel reactors. The latest mechanistic aspects of the water-gas shift reaction and preferential CO oxidation over gold-based catalysts from density functional theory calculations are noted because of their essential role in discovering novel highly efficient catalysts.

Pinpointing the active sites and reaction mechanism of CO oxidation on NiO

CO oxidation on NiO by different oxygen species was investigated using a global pathway searching method.