Support-Induced unusual size dependence of Pd catalysts in chemoselective hydrogenation of para-chloronitrobenzene

Isolation, structural characterization of (1 → 4), (1 → 6)-α-D-glucan from Dioscorea Alata and synthesis and catalytic activity studies of (1 → 4), (1 → 6)-α-D-glucan derived carbon dots

Herein, a straightforward, productive protocol was adopted for the synthesis of carbon dots (CDs) by a simple microwave-assisted technique from (1 → 4), (1 → 6)-α-D-glucan polysaccharide (DAPS). The isolation and structural characterization of (1 → 4), (1 → 6)-α-D-glucan from the aqueous extracting of the Diascorea Alata was described here. The photo-physical and morphological studies of the prepared high quantum yield (27.70 %) CDs were systematically characterized using different analytical techniques: TEM, DLS, XPS, XRD, FT-IR, TCSPC, EDX, Fluorescence and UV-vis spectroscopy. In our study the carbon dots (CDs) obtained are non-toxic, highly water-soluble, spherical-shaped negatively charged particles with an average diameter of 3.28 nm. The photo-catalytic activity of carbon dots (CDs) was tested under the sunlight for photo-degradation of crystal violet (CV), a pollutant organic dye. Carbon dots (CDs) showed outstanding results regarding the photo degradation of CV (achieving 99.9 % degradation within 8 min) under sunlight.

From single atoms to nanoparticles: size effect on Pd/C-catalyzed hydrogenation of 2,5-furandicarboxylic acid

In this study, five catalysts with Pd particle sizes ranging from single atoms to nanoclusters and nanoparticles were synthesized by controlling the Pd loading amount and preparation methods, and applied in the hydrogenation of FDCA to THFDCA. Furthermore, kinetic models were established. Notably, the nanocluster catalyst demonstrated relatively high hydrogenation activity.

Hypoxia Reversion and STING Pathway Activation through Large Mesoporous Nanozyme for Near-Infrared-II Light Amplified Tumor Polymetallic-Immunotherapy

cGAS/STING pathway, which is highly related to tumor hypoxia, is considered as a potential target for remodeling the immunosuppressive microenvironment of solid tumors. Metal ions, such as Mn2+, activate the cGAS/STING pathway, but their efficacy in cancer therapy is limited by insufficient effect on immunogenic tumor cell death of a single ion. Here, we evaluate the association between tumor hypoxia and cGAS/STING inhibition and report a polymetallic-immunotherapy strategy based on large mesoporous trimetal-based nanozyme (AuPdRh) coordinated with Mn2+ (Mn2+@AuPdRh) to activate cGAS/STING signaling for robust adaptive antitumor immunity. Specifically, the inherent CAT-like activity of this polymetallic Mn2+@AuPdRh nanozyme decomposes the endogenous H2O2 into O2 to relieve tumor hypoxia induced suppression of cGAS/STING signaling. Moreover, the Mn2+@AuPdRh nanozyme displays a potent near-infrared-II photothermal effect and strong POD-mimic activity; and the generated hyperthermia and •OH radicals synergistically trigger immunogenic cell death in tumors, releasing abundant dsDNA, while the delivered Mn2+ augments the sensitivity of cGAS to dsDNA and activates the cGAS-STING pathway, thereby triggering downstream immunostimulatory signals to kill primary and distant metastatic tumors. Our study demonstrates the potential of metal-based nanozyme for STING-mediated tumor polymetallic-immunotherapy and may inspire the development of more effective strategies for cancer immunotherapy.

Significantly enhanced catalytic performance of Pd nanocatalyst on AlOOH featuring abundant solid surface frustrated Lewis pair for improved hydrogen activation

The catalytic performance of a catalyst is significantly influenced by its ability to activate hydrogen. Constructing frustrated Lewis pairs (FLPs) with the capacity for hydrogen dissociation on non-reducible supports remains a formidable challenge. Herein, we employed a straightforward method to synthesize a layered AlOOH featuring abundant OH defects suitable for constructing solid surface frustrated Lewis pair (ssFLP). The results indicated that the AlOOH-80 (synthesized at 80 °C) possessed an appropriate crystalline structure conducive to generating numerous OH defects, which facilitated the formation of ssFLP. This was further evidenced by the minimal water adsorption in the AlOOH-80, inversely correlated with the quantity of defects in the catalyst. As expected, the Pd loaded onto AlOOH (Pd/AlOOH-80) exhibited excellent catalytic activity in hydrogenation reactions, attributed to abundant defects available for constructing ssFLP. Remarkably, the Pd/AlOOH-80 catalyst, with larger-sized Pd nanoparticles, displayed notably superior activity compared to commercial Pd/Al2O3 and Pd/C, both featuring smaller-sized Pd nanoparticles. Evidently, under the influence of ssFLP, the size effect of Pd nanoparticles did not dominate, highlighting the pivotal role of ssFLP in enhancing catalytic performance. This catalyst also exhibited exceptionally high stability, indicating its potential for industrial applications.

Iron-Based Catalysts with Oxygen Vacancies Obtained by Facile Pyrolysis for Selective Hydrogenation of Nitrobenzene

The development of preparation strategies for iron-based catalysts with prominent catalytic activity, stability, and cost effectiveness is greatly significant for the field of catalytic hydrogenation but still remains challenging. Herein, a method for the preparation of iron-based catalysts by the simple pyrolysis of organometallic coordination polymers is described. The catalyst Fe@C-2 with sufficient oxygen vacancies obtained in specific coordination environment exhibited superior nitro hydrogenation performance, acid resistance, and reaction stability. Through solvent effect experiments, toxicity experiments, TPSR, and DFT calculations, it was determined that the superior activity of the catalyst was derived from the contribution of sufficient oxygen vacancies to hydrogen activation and the good adsorption ability of FeO on substrate molecules.

Mesoporous α-Al2O3-supported PdCu bimetallic nanoparticle catalyst for the selective semi-hydrogenation of alkynes

The selective hydrogenation of alkynes to alkenes is widely applied in the chemical industry; nevertheless, achieving highly selective hydrogenation with high catalytic activity is considerably challenging. Herein, ultrafine PdCu bimetallic nanoparticles encapsulated by high-surface-area mesoporous α-Al2O3 were prepared by high-temperature calcination-reduction using a porous organic framework (POF) as the template. As-obtained PdCu@α-Al2O3 exhibited a high selectivity of 95% for the semi-hydrogenation of phenylacetylene as a probe reaction under mild reaction conditions. The separation of continuous Pd atoms and modification of the Pd electronic state by Cu atoms suppressed β-hydride formation and alkene adsorption, contributing to high selectivity for the catalytic hydrogenation of alkynes. The catalytic activity was maintained after 7 cycles due to the strong interaction between the PdCu bimetallic nanoparticles and α-Al2O3 as well as the encapsulation effect of mesoporous α-Al2O3. Thus, the current work provides a facile strategy for fabricating high-surface-area mesoporous α-Al2O3-supported catalysts for industrial catalysis applications.

Possible handle for broadening the catalysis regime towards low temperatures: proof of concept and mechanistic studies with CO oxidation on surface modified Pd-TiO2

The present work demonstrates the effect of temperature-dependent surface modification (SM) treatment and its influence in broadening the catalysis regime with Pd-TiO2 catalysts prepared by various methods. Due to SM induced changes, a shift in the onset of CO oxidation activity as well as broadening of the oxidation catalysis regime by 30 to 65 K to lower temperatures is observed compared to the temperature required for virgin counterparts. SM carried out at 523 K for PdPhoto-TiO2 exhibits the lowest onset (10% CO2 production - T10) and T100 for CO oxidation at 360 and 392 K, respectively, while its virgin counterpart shows T10 and T100 at 393 and 433 K, respectively. The SMd Pd-TiO2 catalysts were investigated using X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and atomic force microscopy (AFM). It is observed that diffusion of atomic oxygen into Pd-subsurfaces leads to SM and changes the nature of the surface significantly. These changes are demonstrated by work function (ϕ), surface potential, catalytic activity, and correlation among them. UPS results demonstrate the maximum increase in ϕ by 0.5 eV for PdPhoto-TiO2 after SM, compared to all other catalysts. XPS study shows a moderate to severe change in the oxidation states of Pd due to atomic oxygen diffusion into the subsurface layers of Pd. Kelvin probe force microscopy (KPFM) study also reveals corroborating evidence that the surface potential increases linearly with increasing temperature deployed for SM up to 523 K, followed by a marginal decrease at 573 K. The ϕ measured by KPFM and UPS shows a similar trend and correlates well with the changes in catalysis observed. Our results indicate that there is a strong correlation between surface physical and chemical properties, and ϕ changes could be considered as a global marker for chemical reactivity.

Conjugated dual size effect of core-shell particles synergizes bimetallic catalysis

Core-shell bimetallic nanocatalysts have attracted long-standing attention in heterogeneous catalysis. Tailoring both the core size and shell thickness to the dedicated geometrical and electronic properties for high catalytic reactivity is important but challenging. Here, taking Au@Pd core-shell catalysts as an example, we disclose by theory that a large size of Au core with a two monolayer of Pd shell is vital to eliminate undesired lattice contractions and ligand destabilizations for optimum benzyl alcohol adsorption. A set of Au@Pd/SiO₂ catalysts with various core sizes and shell thicknesses are precisely fabricated. In the benzyl alcohol oxidation reaction, we find that the activity increases monotonically with the core size but varies nonmontonically with the shell thickness, where a record-high activity is achieved on a Au@Pd catalyst with a large core size of 6.8 nm and a shell thickness of ~2-3 monolayers. These findings highlight the conjugated dual particle size effect in bimetallic catalysis.

Tuning Particle Sizes and Active Sites of Ni/CeO2 Catalysts and Their Influence on Maleic Anhydride Hydrogenation

Supported metal catalysts are widely used in industrial processes, and the particle size of the active metal plays a key role in determining the catalytic activity. Herein, CeO₂-supported Ni catalysts with different Ni loading and particle size were prepared by the impregnation method, and the hydrogenation performance of maleic anhydride (MA) over the Ni/CeO₂ catalysts was investigated deeply. It was found that changes in Ni loading causes changes in metal particle size and active sites, which significantly affected the conversion and selectivity of MAH reaction. The conversion of MA reached the maximum at about 17.5 Ni loading compared with other contents of Ni loading because of its proper particle size and active sites. In addition, the effects of Ni grain size, surface oxygen vacancy, and Ni–CeO₂ interaction on MAH were investigated in detail, and the possible mechanism for MAH over Ni/CeO₂ catalysts was deduced. This work greatly deepens the fundamental understanding of Ni loading and size regimes over Ni/CeO₂ catalysts for the hydrogenation of MA and provides a theoretical and experimental basis for the preparation of high-activity catalysts for MAH.

Platinum clusters anchored on sulfur-doped ordered mesoporous carbon for chemoselective hydrogenation of halogenated nitroarenes

Chemoselective hydrogenation of unsaturated organic compounds is a significant research topic in the catalysis field. Herein, a sulfur-doped ordered mesoporous carbon (SMC) material was prepared to anchor ultrafine platinum (Pt) clusters for the chemoselective hydrogenation of halogenated nitroarenes. The confinement effect of the ordered pores and the strong metal-support interaction caused by Pt clusters and sulfur atoms, efficiently suppress the aggregation and regulate the electronic states of the ultrafine Pt clusters. Thus, the hydrogenation of parachloronitrobenzene (p-CNB) shows high selectivity catalyzed by the ultrafine Pt clusters with electron-rich states. Meanwhile, the catalytic performance of the hydrogenation reaction catalyzed by Pt/SMC is capable of being maintained after at least 5 cycles, and the catalytic universality can also be applied to different halogenated nitroarenes hydrogenation. Therefore, this study may promote the research into the construction of noble metal-based catalysts for chemoselective hydrogenation reactions in green and sustainable chemical processes.

Ultrafine PdCo bimetallic nanoclusters confined in N-doped porous carbon for the efficient semi-hydrogenation of alkynes

Ultrafine PdCo bimetallic nanoclusters with Co atom-modified Pd active sites were highly dispersed and confined in an m-NC material for selective semi-hydrogenation of alkynes to alkenes.

Facile and template-free synthesis of porous carbon modified with FeOx for transfer hydrogenation of nitroarenes

Porous carbon modified with FeOx was developed using an in situ activation method for transfer hydrogenation of nitroarenes.

Toward High Selectivity Aniline Synthesis Catalysis at Elevated Temperatures

In connection with an initiative to enhance heat recovery from the large-scale operation of a heterogeneously catalyzed nitrobenzene hydrogenation process to produce aniline, it is necessary to operate the process at elevated temperatures (>100 °C), a condition that can compromise aniline selectivity. Alumina-supported palladium catalysts are selected as candidate materials that can provide sustained aniline yields at elevated temperatures. Two Pd/Al₂O₃ catalysts are examined that possess comparable mean Pd particle sizes (∼5 nm) for different Pd loading: 5 wt % Pd/Al₂O₃ and 0.3 wt % Pd/Al₂O₃. The higher Pd loading sample represents a reference catalyst for which the Pd crystallite morphology has previously been established. The lower Pd loading technical catalyst more closely corresponds to industrial specifications. The morphology of the Pd crystallites of the 0.3 wt % Pd/Al₂O₃ sample is explored by means of temperature-programmed infrared spectroscopy of chemisorbed CO. Reaction testing over the range of 60–180 °C shows effectively complete nitrobenzene conversion for both catalysts but with distinction in their selectivity profiles. The low loading catalyst is favored as it maximizes aniline selectivity and avoids the formation of overhydrogenated products. A plot of aniline yield as a function of WHSV for the 0.3 wt % Pd/Al₂O₃ catalyst at 100 °C yields a “volcano” like curve, indicating aniline selectivity to be sensitive to residence time. These observations are brought together to provide an indication of an aniline synthesis catalyst specification suited to a unit operation equipped for enhanced heat transfer.