Theoretical insights into furfural reduction to furfuryl alcohol via the catalytic hydrogen transfer reaction catalyzed by cations exchanged zirconium-containing zeolites

Synthesis and Characterization of Zeolite A from Industrial Fly Ash as a Green, Cost-Effective Cd2+ and Pb2+ Adsorbent for Wastewater Applications

According to the large amount of fly ash waste generated from the use of lignite coal as the primary fuel for electricity generation in the Mae Moh district of Lampang province, Thailand, efforts have been made in waste management to reduce and repurpose this industrial byproduct. In this study, lignite coal fly ash was used to synthesize zeolite A adsorbents for the treatment of wastewater contaminated with heavy metals. Characterization of the synthesized zeolite using XRD, XRF, BET, and SEM methods confirmed that it is zeolite A, with a calculated Si/Al molar ratio of approximately 1.19, closely matching the theoretical ratio of zeolite A. This zeolite A exhibited a high crystalline phase and a mesoporous structure, having a specific surface area of 37.10 m2/g and a total pore volume of 0.06 cm3/g. The performance of this zeolite A was evaluated for the adsorption of Cd2+ and Pb2+ in prepared solutions. The removal efficiencies of zeolite A for Cd2+ and Pb2+ were 99.65% ± 0.1% and 93.90% ± 0.5%, with maximum adsorption capacities of 17.3 ± 0.6 and 8.8 ± 0.1 mg/g, respectively. Additionally, zeolite A demonstrated reusability for the adsorption of Cd2+ and Pb2+, maintaining a removal efficiency of 80.52% ± 0.1% for Cd2+ over five reuse cycles, and 96.83% ± 0.7% for Pb2+ over one reuse cycle. The adsorption of Cd2+ and Pb2+ by zeolite A followed the Langmuir isotherm model and pseudo-second-order kinetic model. Moreover, the adsorption of Cd2+ and Pb2+ by zeolite A was found to be a spontaneous, endothermic process, as evidenced by increasingly negative Gibbs free energy change (ΔG°) values with rising temperature. Density functional theory (DFT) calculations were also performed to investigate the binding of Cd2+ and Pb2+ ions to zeolite A, providing insight into why Cd2+ exhibits a slightly higher affinity than Pb2+. The results showed that Cd2+ ions have a marginally greater affinity for zeolite A compared to Pb2+ (-85.72 vs -85.39 kcal/mol), which aligns with experimental findings. This study offers an alternative approach for reducing industrial waste by repurposing it for valuable applications, contributing to sustainable waste management practices that align with the principles of the bio-circular-green economy.

The Role of Frustrated Lewis Pair in Catalytic Transfer Hydrogenation of Furfural using Nickel Single-Atom Catalysts: A Theoretical Study

The burgeoning field of frustrated Lewis pair (FLP) heterogeneous catalysts has garnered significant interest in recent years, primarily due to their inherent ability to activate H-source molecules, thereby facilitating hydrogenation reactions. In this study, non-precious transition metal atoms were anchored onto several models of pyridinic nitrogen incorporated graphene sheet. Theoretical calculations substantiated energy barriers as low as 0.10 eV for isopropanol activation, thereby positioning these catalysts as highly promising candidates for catalytic transfer hydrogenation of furfural. Electronic structure analyses revealed that the H-O bond breakage in isopropanol molecules was significantly facilitated by the presence of FLP sites within the catalysts. Notably, both Ni-C2N and Ni-N6-C demonstrated exceptional potential as selective catalysts for the hydrogenation of furfural into furfuryl alcohol, exhibiting remarkably low barriers of only 0.65-0.72 eV for the rate-determining steps. The findings in this study are helpful to design FLP containing single atom catalysts for hydrogenation reactions.

Synthesis and Catalytic Applications of Advanced Sn- and Zr-Zeolites Materials

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water-tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn- and Zr-containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10-MR medium pore zeolites (FER, MCM-56, MEL, MFI, MWW), 12-MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14-MR extra-large pore UTL zeolite. This review about Sn- and Zr-containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Mechanism of Catalytic Transfer Hydrogenation for Furfural Using Single Ni Atom Catalysts Anchored to Nitrogen-Doped Graphene Sheets

Catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes using single metal atom catalysts supported on nitrogen-incorporated graphene sheet (M-N_x-Gr) materials has attracted increasing attention recently, yet the reaction mechanism remains to be explored. Compared to the Ni-N₄-Gr model in which the dissociation of isopropanol is highly unfavorable as a result of steric hindrance and inertness of the Ni-N₄ site embedded in graphene, the Ni-N₃ site in Ni-N₃-Gr is more active and facilitates the formation of *H with isopropanol as the H donor, where the dissociation of H from isopropanol with an energy barrier of 0.83 eV is the rate-determining step. An alternative reaction path starts from the coadsorption of isopropanol and furfural molecules at the Ni-N₃ site, followed by a direct hydrogen transfer between the two molecules; however, the rate-determining step has a much higher energy barrier of 1.32 eV. Our calculations suggest that the hydrogenation of the aldehyde group is kinetically more favorable than the C═C hydrogenation, revealing the high chemoselectivity of furfural to furfuryl alcohol. Our investigations reveal that the CTH mechanism using the Ni-N₃-Gr catalyst is different from that on traditional metal oxides, where the former has only one single active site, while two active sites are required for the latter. The proposed reaction mechanism of CTH for furfural in this study should be helpful to guide the design of single metal atom catalysts with appropriate N coordination for application in chemoselective hydrogenation reactions.