Slowing the Kinetics of Alumina Sol-Gel Chemistry for Controlled Catalyst Overcoating and Improved Catalyst Stability and Selectivity

Advances in morphology-controlled alumina and its supported Pd catalysts: synthesis and applications

Alumina materials, as one of the cornerstones of the modern chemical industry, possess physical and chemical properties that include excellent mechanical strength and structure stability, which also make them highly suitable as catalyst supports. Alumina-supported Pd-based catalysts with the advantages of exceptional catalytic performance, flexible regulated surface metal/acid sites, and good regeneration ability have been widely used in many traditional chemical industry fields and have also shown great application prospects in emerging fields. This review aims to provide an overview of the recent advances in alumina and its supported Pd-based catalysts. Specifically, the synthesis strategies, morphology transformation mechanisms, and structural properties of alumina with various morphologies are comprehensively summarized and discussed in-depth. Then, the preparation approaches of Pd/Al2O3 catalysts (impregnation, precipitation, and other emerging methods), as well as the metal-support interactions (MSIs), are revisited. Moreover, Some promising applications have been chosen as representative reactions in fine chemicals, environmental purification, and sustainable development fields to highlight the universal functionality of the alumina-supported Pd-based catalysts. The role of the Pd species, alumina support, promoters, and metal-support interactions in the enhancement of catalytic performance are also discussed. Finally, some challenges and upcoming opportunities in the academic and industrial application of the alumina and its supported Pd-based are presented and put forward.

Ternary Alloys Enable Efficient Production of Methoxylated Chemicals via Selective Electrocatalytic Hydrogenation of Lignin Monomers

We explore the selective electrocatalytic hydrogenation of lignin monomers to methoxylated chemicals, of particular interest, when powered by renewable electricity. Prior studies, while advancing the field rapidly, have so far lacked the needed selectivity: when hydrogenating lignin-derived methoxylated monomers to methoxylated cyclohexanes, the desired methoxy group (-OCH₃) has also been reduced. The ternary PtRhAu electrocatalysts developed herein selectively hydrogenate lignin monomers to methoxylated cyclohexanes-molecules with uses in pharmaceutics. Using X-ray absorption spectroscopy and in situ Raman spectroscopy, we find that Rh and Au modulate the electronic structure of Pt and that this modulating steers intermediate energetics on the electrocatalyst surface to facilitate the hydrogenation of lignin monomers and suppress C-OCH₃ bond cleavage. As a result, PtRhAu electrocatalysts achieve a record 58% faradaic efficiency (FE) toward 2-methoxycyclohexanol from the lignin monomer guaiacol at 200 mA cm^-2, representing a 1.9× advance in FE and a 4× increase in partial current density compared to the highest productivity prior reports. We demonstrate an integrated lignin biorefinery where wood-derived lignin monomers are selectively hydrogenated and funneled to methoxylated 2-methoxy-4-propylcyclohexanol using PtRhAu electrocatalysts. This work offers an opportunity for the sustainable electrocatalytic synthesis of methoxylated pharmaceuticals from renewable biomass.

Thermal Shock Synthesis of Nanocatalyst by 3D-Printed Miniaturized Reactors

High temperature synthesis and treatments are ubiquitous in chemical reactions and material manufacturing. However, conventional sintering furnaces are bulky and inefficient with a narrow temperature range (<1500 K) and slow heating rates (<100 K min^-1 ), which are undesirable for many applications that require transient heating to produce ideal nanostructures. Herein, a 3D-printed, miniaturized reactor featuring a dense micro-grid design is developed to maximize the material contact and therefore acheive highly efficient and controllable heating. By 3D printing, a versatile, miniaturized reactor with microscale features can be constructed, which can reach a much wider temperature range (up to ≈3000 K) with ultrafast heating/cooling rates of ≈10⁴ K s^-1 . To demonstrate the utility of the design, rapid and batch synthesis of Ru nanoparticles supported in ordered mesoporous carbon is performed by transient heating (1500 K, 500 ms). The resulting ultrafine and uniform Ru nanoparticles (≈2 nm) can serve as a cathode in Li-CO₂ batteries with good cycling stability. The miniaturized reactor, with versatile shape design and highly controllable heating capabilities, provides a platform for nanocatalyst synthesis with localized and ultrafast heating toward high temperatures that is otherwise challenging to achieve.

Atomic Layer Deposition on Dispersed Materials in Liquid Phase by Stoichiometrically Limited Injections

Atomic layer deposition (ALD) is a well-established vapor-phase technique for depositing thin films with high conformality and atomically precise control over thickness. Its industrial development has been largely confined to wafers and low-surface-area materials because deposition on high-surface-area materials and powders remains extremely challenging. Challenges with such materials include long deposition times, extensive purging cycles, and requirements for large excesses of precursors and expensive low-pressure equipment. Here, a simple solution-phase deposition process based on subsequent injections of stoichiometric quantities of precursor is performed using common laboratory synthesis equipment. Precisely measured precursor stoichiometries avoid any unwanted reactions in solution and ensure layer-by-layer growth with the same precision as gas-phase ALD, without any excess precursor or purging required. Identical coating qualities are achieved when comparing this technique to Al₂ O₃ deposition by fluidized-bed reactor ALD (FBR-ALD). The process is easily scaled up to coat >150 g of material using the same inexpensive laboratory glassware without any loss in coating quality. This technique is extended to sulfides and phosphates and can achieve coatings that are not possible using classic gas-phase ALD, including the deposition of phosphates with inexpensive but nonvolatile phosphoric acid.