Formation of different promoted metallic phases in PtFe and PtSn catalysts supported on carbonaceous materials used for selective hydrogenation

Unsupported Nanoporous Platinum-Iron Bimetallic Catalyst for the Chemoselective Hydrogenation of Halonitrobenzenes to Haloanilines

An unsupported nanoporous platinum-iron bimetallic catalyst (PtFeNPore) was prepared with an electrochemical dealloying technique. Its structure and composition were characterized through various measurement methods, such as X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS). An intermetallic compound and iron oxide species were both found in the PtFeNPore catalyst. The nanoporous structure and Lewis acidity (caused by iron oxide species) of the PtFeNPore catalyst resulted in superior catalytic activity and high selectivity. The PtFeNPore-catalyzed hydrogenation of various halonitrobenzenes proceeded successfully under mild reaction conditions and produced good to excellent yields of the corresponding haloanilines with high selectivity. PtFeNPore can be recycled through magnetic separation easily and reused five times without significant deactivation.

Platinum and cobalt intermetallic nanoparticles confined within MIL-101(Cr) for enhanced selective hydrogenation of the carbonyl bond in α,β-unsaturated aldehydes: synergistic effects of electronically modified Pt sites and Lewis acid sites

PtCo/MIL-101(Cr) with high uniform dispersion Pt–Co IMNs synthesized by a polyol reduction method show higher activity for selective catalytic hydrogenation of α,β-unsaturated aldehydes due to the synergistic effect of PtCo and MIL-101(Cr) support.

Sn-doped Pt catalyst supported on hierarchical porous ZSM-5 for the liquid-phase hydrogenation of cinnamaldehyde

3Pt0.05Sn/HPZSM-5 serves as a much more active and recyclable catalyst for the liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.

Control of crystallographic phases and surface characterization of intermetallic platinum tin nanoparticles

Colloidal synthesis and characterization of intermetallic tin-rich platinum–tin nanoparticles with detailed surface characterization.

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.

In situ dynamic tracking of heterogeneous nanocatalytic processes by shell-isolated nanoparticle-enhanced Raman spectroscopy

Surface molecular information acquired in situ from a catalytic process can greatly promote the rational design of highly efficient catalysts by revealing structure-activity relationships and reaction mechanisms. Raman spectroscopy can provide this rich structural information, but normal Raman is not sensitive enough to detect trace active species adsorbed on the surface of catalysts. Here we develop a general method for in situ monitoring of heterogeneous catalytic processes through shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) satellite nanocomposites (Au-core silica-shell nanocatalyst-satellite structures), which are stable and have extremely high surface Raman sensitivity. By combining operando SHINERS with density functional theory calculations, we identify the working mechanisms for CO oxidation over PtFe and Pd nanocatalysts, which are typical low- and high-temperature catalysts, respectively. Active species, such as surface oxides, superoxide/peroxide species and Pd–C/Pt–C bonds are directly observed during the reactions. We demonstrate that in situ SHINERS can provide a deep understanding of the fundamental concepts of catalysis.

Rational design of heterogeneous catalysts requires molecular understanding of catalytic processes. Here, the authors attach PtFe and Pd nanocatalysts to Raman signal-enhancing Au-silica nanoparticles, allowing them to spectroscopically observe the active species and bonds involved in CO oxidation in real time.

Insight into the structure evolution and the associated catalytic behavior of highly dispersed Pt and PtSn catalysts supported on La2O2CO3 nanorods

This work reports the composition-dependent structure evolution and the associated catalytic behavior of PtSn catalysts supported on La₂O₂CO₃ nanorods.

Efficient Pt–FeOx/TiO2@SBA-15 catalysts for selective hydrogenation of cinnamaldehyde to cinnamyl alcohol

Pt–FeO_x/TiO₂@SBA-15 serves as an efficient and recyclable catalyst for liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions.

Metal-organic frameworks as selectivity regulators for hydrogenation reactions

Owing to the limited availability of natural sources, the widespread demand of the flavouring, perfume and pharmaceutical industries for unsaturated alcohols is met by producing them from α,β-unsaturated aldehydes, through the selective hydrogenation of the carbon-oxygen group (in preference to the carbon-carbon group). However, developing effective catalysts for this transformation is challenging, because hydrogenation of the carbon-carbon group is thermodynamically favoured. This difficulty is particularly relevant for one major category of heterogeneous catalyst: metal nanoparticles supported on metal oxides. These systems are generally incapable of significantly enhancing the selectivity towards thermodynamically unfavoured reactions, because only the edges of nanoparticles that are in direct contact with the metal-oxide support possess selective catalytic properties; most of the exposed nanoparticle surfaces do not. This has inspired the use of metal-organic frameworks (MOFs) to encapsulate metal nanoparticles within their layers or inside their channels, to influence the activity of the entire nanoparticle surface while maintaining efficient reactant and product transport owing to the porous nature of the material. Here we show that MOFs can also serve as effective selectivity regulators for the hydrogenation of α,β-unsaturated aldehydes. Sandwiching platinum nanoparticles between an inner core and an outer shell composed of an MOF with metal nodes of Fe³⁺, Cr³⁺ or both (known as MIL-101; refs 19, 20, 21) results in stable catalysts that convert a range of α,β-unsaturated aldehydes with high efficiency and with significantly enhanced selectivity towards unsaturated alcohols. Calculations reveal that preferential interaction of MOF metal sites with the carbon-oxygen rather than the carbon-carbon group renders hydrogenation of the former by the embedded platinum nanoparticles a thermodynamically favoured reaction. We anticipate that our basic design strategy will allow the development of other selective heterogeneous catalysts for important yet challenging transformations.

Enhanced Activity of Supported Ni Catalysts Promoted by Pt for Rapid Reduction of Aromatic Nitro Compounds

To improve the activities of non-noble metal catalysts is highly desirable and valuable to the reduced use of noble metal resources. In this work, the supported nickel (Ni) and nickel-platinum (NiPt) nanocatalysts were derived from a layered double hydroxide/carbon composite precursor. The catalysts were characterized and the role of Pt was analysed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) mapping, and X-ray photoelectron spectroscopy (XPS) techniques. The Ni²⁺ was reduced to metallic Ni⁰ via a self-reduction way utilizing the carbon as a reducing agent. The average sizes of the Ni particles in the NiPt catalysts were smaller than that in the supported Ni catalyst. The electronic structure of Ni was affected by the incorporation of Pt. The optimal NiPt catalysts exhibited remarkably improved activity toward the reduction of nitrophenol, which has an apparent rate constant (K_a) of 18.82 × 10⁻³ s⁻¹, 6.2 times larger than that of Ni catalyst and also larger than most of the reported values of noble-metal and bimetallic catalysts. The enhanced activity could be ascribed to the modification to the electronic structure of Ni by Pt and the effect of exposed crystal planes.

Effect of carbon nanosheets with different graphitization degrees as a support of noble metals on selective hydrogenation of cinnamaldehyde

Effect of carbon nanosheets with different graphitization degrees on the catalytic activity of Pt/CNS and Pd/CNS was investigated in selective hydrogenation of cinnamaldehyde.

Effect of Carbon Supported Pt Catalysts on Selective Hydrogenation of Cinnamaldehyde

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) is of both fundamental and industrial interest. It is of great significance to evaluate the possible differences between different supports arising from metal dispersion and electronic effects, in terms of activity and selectivity. Herein, Pt catalysts on different carbon supports including carbon nanotubes (CNTs) and reduced graphene oxides (RGO) were developed by a simple wet impregnation method. The resultant catalysts were well characterized by XRD, Raman, N2physisorption, TEM, and XPS analysis. Applied in the hydrogenation of cinnamaldehyde, 3.5 wt% Pt/CNT shows much higher selectivity towards cinnamyl alcohol (62%) than 3.5 wt% Pt/RGO@SiO2(48%). The enhanced activity can be ascribed to the high graphitization degree of CNTs and high density of dispersed Pt electron cloud.