Single-atom and small-cluster Pt induced by Sn (IV) sites confined in an LDH lattice for catalytic reforming

Active Pd Catalyst for the Selective Synthesis of Methylated Amines with Methanol

Selective N-methylation of amines with methanol is an important reaction in the synthesis of high-value-added fine chemicals, including dyes, surfactants, pharmaceuticals, agrochemicals, and materials. However, N-methylated amines possess higher reactivities and are prone to further transform into N,N-dimethylated amines. Therefore, it is still a challenge to controllably regulate the selectivity of N-methylation using heterogeneous catalysts without the use of base. Herein, we developed a series of Pd/Zn(Al)O catalysts with abundant basic sites, and the selectivity of N-methylation was controlled by a heterogeneous Pd/Zn(Al)O catalyst with a Zn/Al ratio of 10 and a Pd loading of 0.4 wt % in the pressure of H₂. The experimental results showed that the appropriate basic properties of the catalyst were beneficial to form the desired N-methylated amine. The low loading of Pd in the catalyst was highly dispersed on the support, providing sufficient active sites. These were attributed to the Zn vacancies formed by Al-doped Zn, which were beneficial to form the highly active and stable Pd sites. Furthermore, a series of amines and nitrobenzenes with different functional groups were well tolerated for the selective synthesis of N-methylated amines in the absence of base.

Rational Design and Preparation of Pt-LDH/CeO2 Catalyst for High-Efficiency Photothermal Catalytic Oxidation of Toluene

Volatile organic compounds (VOCs) are attracting much more attention due to their contributions to air pollution and human health problems. Photothermal catalytic oxidation is considered as an energy-saving method for the removal of VOCs. However, the efficiency of the photothermal catalytic system is still suffering from the low activity of the catalyst due to its poor response to visible light and low efficiency of charge separation. Here, few-layer CoAl-LDH (layered double hydroxide) was prepared as an advantageous support for loading Pt nanoparticles to obtain Pt-LDH, which were coated on CeO₂ nanoparticles. Type II heterojunctions were formed on the interface of LDH and CeO₂. In photocatalysis, the hot electrons will move to CeO₂, which is better at the activation of O₂ molecules, and holes will concentrate on the LDHs, which have plenty of hydroxyls to generate •OH radicals. Furthermore, the Schottky heterojunctions between LDH and Pt nanoparticles benefit the improvement of light absorption by the localized surface plasmon resonance of Pt nanoparticles. As a consequence, a high removal rate of toluene (75.7%) at a weight-hourly space velocity of 23340 mL/(g·h) under visible light irradiation (160 mW/cm², λ > 400 nm) at room temperature was achieved over the Pt-LDH/CeO₂ catalyst. The catalyst design provides a useful method to prepare high-efficiency photothermal catalysts.

Topology dependent modification of layered double hydroxide for therapeutic and diagnostic platform

Layered double hydroxide is a family of two-dimensional materials with wide range of compositions. Recently, its ability to accommodate various chemical species and biocompatibility have been attracted in the biomedical applications to develop drug delivery system and nanodiagnostics. In this review, we categorized biomedical approaches of layered double hydroxide with respect to the three topologies of, namely, interlayer space, outer surface with particle edge, and the lattice points. There have been extensive researches on the intercalation of drug or tracing to make use of interlayer space of layered double hydroxide for drug stabilization, sustained release, cellular delivery and etc. Outer surface or edge has been utilized to immobilization of large therapeutic moieties and to attach tracing moiety. Lattice points consisting of various metal species could be utilized for the specific metal species like paramagnetic elements or radioisotopes. Based on these topologies in layered double hydroxide, both the synthetic routes and the achieved functionalities in terms of biomedical application will be discussed.

The in situ growth of Mg–Al hydrotalcite on spherical alumina and its application as a support of a Pt-based catalyst for isobutane dehydrogenation

The in situ growth of Mg–Al hydrotalcite on spherical alumina and its application in catalytic dehydrogenation with a Pt-based catalyst.

Mercaptosilane-assisted synthesis of highly dispersed and stable Pt nanoparticles on HL zeolites for enhancing hydroisomerization of n-hexane

Pt/HL-SH catalysts were synthesized by a facile mercaptosilane-assisted in situ synthesis approach and exhibited better catalytic performance in n-hexane hydroisomerization.

Single site Fe on the (110) surface of γ-Al2O3: insights from a DFT study including the periodic boundary approach

Examination of the stable (110) surface of γ-alumina reveals that there are three different types of sites available to host a single Fe atom. With the carefully calibrated density functional approach (M12-L/SV), three types of Fe single sites on the (110) surface of γ-alumina have been investigated under the periodic boundary conditions. The most stable Fe replacement site on the (110) surface of γ-alumina has been found to be represented by the tri-coordinated Fe_I position with the quartet spin state. The replacement of Al by Fe atoms at the Al site leads to charge redistributions of the neighboring O atoms. However, sublayer charge distribution is less affected. A significant contribution of p orbitals of the O atoms in the surface phase to the LUMO has been found for the tri-coordinated Fe_I substitution on the (110) surface. The corresponding oxygen atoms (O_A and O_A1) have been activated due to the existence of Fe_I in their neighborhood. The loosened neighboring Al_III-O_A bonds match this activation. This activation of O suggests the existence of an important source of the reactive O during the Fe catalytic oxidation of CO processes.

Propane dehydrogenation: catalyst development, new chemistry, and emerging technologies

This review describes recent advances in the propane dehydrogenation process in terms of emerging technologies, catalyst development and new chemistry.

Atomic Pt-Catalyzed Heterogeneous Anti-Markovnikov C-N Formation: Pt10 Activating N-H for Pt1δ+-Activated C═C Attack

C-N formation is of great significance to synthetic chemistry, as N-containing products are widely used in chemistry, medicine, and biology. Addition of an amine to an unsaturated carbon-carbon bond is a simple yet effective route to produce new C-N bonds. But how to effectively conduct an anti-Markovnikov addition with high selectivity has been a great challenge. Here, we proposed a strategy for highly regioselective C-N addition via hydroamination by using supported Pt. It has been identified that atomic-scale Pt is the active site for C-N addition with Pt₁²⁺ for Markovnikov C-N formation and atomic Pt (Pt₁^δ+ and Pt₁⁰) contributing to anti-Markovnikov C-N formation. A selectivity of up to 92% to the anti-Markovnikov product has been achieved with atomic Pt in the addition of styrene and pyrrolidine. A cooperating catalysis for the anti-Markovnikov C-N formation between Pt₁^δ+ and Pt₁⁰ has been revealed. The reaction mechanism has been studied by EPR spectra and in situ FT-IR spectra of adsorption/desorption of styrene and/or pyrrolidine. It has been demonstrated that Pt₁⁰ activates amine to be electrophilic, while Pt₁^δ+ activates C═C by π-bonding to make β-C nucleophilic. The attack of nucleophilic β-C to electrophilic amine affords the anti-Markovnikov addition. This strategy proves highly effective to a variety of substrates in anti-Markovnikov C-N formation, including aromatic/aliphatic amines reacting with aromatic olefins, aromatic/aliphatic olefins with aromatic amines, and linear aliphatic olefins with secondary aliphatic amines. It is believed that the results provide evidence for the function of varied chemical states in monatomic catalysis.

Effect of Reduction Atmosphere on Structure and Catalytic Performance of PtIn/Mg(Al)O/ZnO for Propane Dehydrogenation

The effect of reduction atmospheres, H2/N2, C3H8/H2/N2, C3H8 and CO, on the structure and propane direct dehydrogenation performance of PtIn/Mg(Al)O/ZnO catalyst derived from ZnO-supported PtIn-hydrotalcite was studied. The physicochemical properties of the as-prepared and used catalytic system were characterized by various characterization methods. The results show that the dehydrogenation performance, especially the stability of the PtIn/Mg(Al)O/ZnO catalyst, was significantly improved along with the change in reduction atmosphere. The highest catalytic activity (51% of propane conversion and 97% propylene selectivity), resistance toward coke deposition, and stability for more than 30 h were achieved with the H2/N2-reduced catalyst. The optimal dehydrogenation performance and coke resistance are mainly related to the high Pt dispersion and In0/In3+ molar ratio, strong Pt–In interaction and small metal particle size, depending on the nature of the reduction atmospheres. The reconstruction of meixnerite favors the stability and coke resistance to some extent.

Selective hydrogenation of 2-pentenal using highly dispersed Pt catalysts supported on ZnSnAl mixed metal oxides derived from layered double hydroxides

Highly dispersed Pt catalysts supported on ZnSnAl mixed metal oxides showed high selectivity for 2-pentenol in selective hydrogenation of 2-pentenal.

Glycerol aerobic oxidation to glyceric acid over Pt/hydrotalcite catalysts at room temperature

Glycerol (GLY) aerobic oxidation in an aqueous solution is one of the most prospective pathways in biomass transformation, where the supported catalysts based on noble metals (mainly Au, Pd, Pt) are most commonly employed. Herein, Pt nanoparticles supported on rehydrated Mg_xAl₁-hydrotalcite (denoted as re-Mg_xAl₁-LDH-Pt) were prepared via impregnation-reduction method followed by an in situ rehydration process, which showed high activity and selectivity towards GLY oxidation to produce glyceric acid (GLYA) at room temperature. The metal-support interfacial structure and catalyst basicity were modulated by changing the Mg/Al molar ratio of the hydrotalcite precursor, and the optimal performance was achieved on re-Mg₆Al₁-LDH-Pt with a GLY conversion of 87.6% and a GLYA yield of 58.6%, which exceeded the traditional activated carbon and oxide supports. A combinative study on structural characterizations (XANES, CO-FTIR spectra, and benzoic acid titration) proves that a higher Mg/Al molar ratio promotes the formation of positively charged Pt^δ+ species at metal-support interface, which accelerates bond cleavage of α-C-H and improves catalytic activity. Moreover, a higher Mg/Al molar ratio provides a stronger basicity of support that contributes to the oxidation of terminal-hydroxyl and thus enhances the selectivity of GLYA. This catalyst with tunable metal-support interaction shows prospective applications toward transformation of biomass-based polyols.

Pt/ZrO2 Prepared by Atomic Trapping: An Efficient Catalyst for the Conversion of Glycerol to Lactic Acid with Concomitant Transfer Hydrogenation of Cyclohexene

A series of heterogeneous catalysts consisting of highly dispersed Pt nanoparticles supported on nanosized ZrO₂ (20 to 60 nm) was synthesized and investigated for the one-pot transfer hydrogenation between glycerol and cyclohexene to produce lactic acid and cyclohexane, without any additional H₂. Different preparation methods were screened, by varying the calcination and reduction procedures with the purpose of optimizing the dispersion of Pt species (i.e., as single-atom sites or extra-fine Pt nanoparticles) on the ZrO₂ support. The Pt/ZrO₂ catalysts were characterized by means of transmission electron microscopy techniques (HAADF-STEM, TEM), elemental analysis (ICP-OES, EDX mapping), N₂-physisorption, H₂ temperature-programmed-reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Based on this combination of techniques it was possible to correlate the temperature of the calcination and reduction treatments with the nature of the Pt species. The best catalyst consisted of subnanometer Pt clusters (<1 nm) and atomically dispersed Pt (as Pt²⁺ and Pt⁴⁺) on the ZrO₂ support, which were converted into extra-fine Pt nanoparticles (average size = 1.4 nm) upon reduction. These nanoparticles acted as catalytic species for the transfer hydrogenation of glycerol with cyclohexene, which gave an unsurpassed 95% yield of lactic acid salt at 96% glycerol conversion (aqueous glycerol solution, NaOH as promoter, 160 °C, 4.5 h, at 20 bar N₂). This is the highest yield and selectivity of lactic acid (salt) reported in the literature so far. Reusability experiments showed a partial and gradual loss of activity of the Pt/ZrO₂ catalyst, which was attributed to the experimentally observed aggregation of Pt nanoparticles.

Highly Dispersed Single-Atom Pt and Pt Clusters in the Fe-Modified KL Zeolite with Enhanced Selectivity for n-Heptane Aromatization

Conversion of straight-chain paraffins into aromatics is particularly attractive but extremely challenging in the oil refining industry. Constructing the Pt-supported catalysts with high aromatic selectivity is vital. Here, we report a strategy to use Fe-modified KL zeolites to improve the Pt atom utilization efficiency and anchor them inside KL zeolite channels via atomic-layer deposition technique. A combination of highly dispersed single-atom Pt and electron-rich Pt clusters is fabricated on the KL zeolite through the creation of proper nucleation sites. The resulted catalyst (PtFe-1/KL) exhibits excellent performance for the n-heptane aromatization (90.1% aromatic selectivity) with an apparent activation energy of 131 kJ/mol and much enhanced stability at a relatively lower temperature (420 °C). Experimental analysis and density functional theory calculation demonstrate that the single-atom Pt might play a key role in the initial dehydrogenation of n-heptane to 1-heptene, and the superior stable Pt clusters encapsulated inside Fe-decorated KL zeolite channels accelerate the 1-heptene dehydrocyclization to aromatics. The synergetic interaction between single-atom Pt and Pt clusters enables the PtFe-1/KL catalyst to be one of the most effective n-heptane aromatization catalysts reported to date.

Platinum single-atom catalysts: a comparative review towards effective characterization

This review summaries the characterization techniques for Pt single-atom catalysts and focuses on FT-EXAFS spectroscopy to study the coordination environment of Pt–M for atomically dispersed Pt catalysts on diverse supports.

Framework-confined Sn in Si-beta stabilizing ultra-small Pt nanoclusters as direct propane dehydrogenation catalysts with high selectivity and stability

Highly stable Pt/Sn-Si-beta catalysts were prepared via an improved post-synthesis method, exhibiting high catalytic activity, good selectivity and excellent stability for propane dehydrogenation to propene.

Dispersing Metallic Platinum on Green Rust Enables Effective and Selective Hydrogenation of Carbonyl Group in Cinnamaldehyde

Layered double hydroxides (LDHs), a category of two-dimensional nanostructured layered materials, can be employed widely as supports, catalyst precursors, and actual catalysts in a variety of heterogeneous catalytic reactions. In this work, we reported a series of Fe-containing LDHs-supported Pt-based catalysts for base-free selective hydrogenation of cinnamaldehyde into cinnamyl alcohol. It was revealed that their catalytic performances were closely correlated to the compositions of LDH supports. Especially, highly selective hydrogenation of cinnamaldehyde could be achieved over the Fe(II)-Fe(III)-LDH (green rust, FeFe-LDH) supported Pt catalyst, with a high cinnamyl alcohol selectivity of about 92% at a conversion of 90% after a reaction of 2 h, superior to other Fe(III)-containing LDHs (e.g., NiFe-LDH, CoFe-LDH, and ZnFe-LDH) supported Pt ones. It was demonstrated that the high catalytic efficiency of Pt/FeFe-LDH mainly originated from highly electron-rich character of metallic Pt species and the presence of surface reductive Fe²⁺ species, thereby being helpful for the chemisorption and activation of carbonyl group in cinnamaldehyde. Moreover, strong interactions between green rust matrix and metallic Pt species could stabilize the surface Pt nanoparticles, thereby inhibiting the metal leaching during the above reaction. The present study illustrates the validity of support control in supported Pt catalysts via tuning the compositions of LDHs, and thus the electronic structure of active metal sites and catalytic performance in the selective hydrogenation of cinnamaldehyde.

Accelerated active phase transformation of NiO powered by Pt single atoms for enhanced oxygen evolution reaction

Phase transformation of electrode materials widely occurs in electrocatalytic reactions. Metal oxides are promising electrocatalysts for the oxygen evolution reaction (OER); their phase transformation is a key step for the multi-electron OER, and requires extra overpotential. However, little attention has been paid to accelerating and enhancing the phase transformation. Here, we report for the first time that single-atom Pt incorporated into the bulk crystalline phase of porous NiO nanocubes (0.5 wt% Pt/NiO) can greatly promote the active phase (NiOOH) evolution. The Pt doping was achieved by a scalable nanocasting approach using SiO2 as the hard template. In comparison with Pt/NiO samples with PtO2 nanoparticles segregated at the NiO surface (1 wt% Pt), as well as atomistic Pt atoms solely bound at the surface by atomic layer deposition, the bulk Pt doping shows the strongest power in facilitating active phase transformation, which leads to improved OER activity with reduced overpotential and Tafel slope. Experiential data revealed that the charge-transfer from Pt to Ni through O leads to a local weaker Ni-O bond. First principles calculations confirmed that rather than acting as an active site for the OER, monatomic Pt effectively increases the phase transformation rate by reducing the migration barrier of nearby Ni atoms. Our discoveries reveal the relationships of the heteroatom doped structure and phase transformation behavior during the electrochemical process and offer a new route for designing high-performance electrocatalysts.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

Synthesis of a highly dispersed CuO catalyst on CoAl-HT for the epoxidation of styrene

Non-noble CuO/CoAl-HT catalyst with high dispersion and rich electronic density exhibits excellent catalytic performance for the epoxidation of styrene.