Small‐Sized Tungsten Nitride Particles Strongly Anchored on Carbon Nanotubes and their Use as Supports for Pt for Methanol Electro‐oxidation

The anchoring of small‐sized WN (tungsten nitride) nanoparticles (NPs) with good dispersion on carbon nanotubes (CNTs) offers an effective means of obtaining promising materials for use in electrocatalysis. Herein, an effective method based on grinding treatment followed by a nitridation process is proposed to realize this goal. In the synthesis, a solution containing H₄[SiO₄(W₃O₉)₄] (SiW₁₂) and CNTs modified with polyethylenimine (PEI‐CNTs) was ground to dryness. Small‐sized WN NPs were anchored onto the CNTs with good dispersion after calcination under NH₃. Under hydrothermal assembly conditions (absence of grinding), WN particles of larger size and with inferior dispersion were obtained, demonstrating the important role of the grinding process. The benefit of the small‐sized WN has been demonstrated by using WN/CNTs as a support for Pt to catalyze the methanol electro‐oxidation reaction. The mass activity of Pt‐WN/CNTs‐G‐70 (where G denotes the grinding treatment, and 70 is the loading amount (%) of WN in the WN/CNTs) was evaluated as about 817 mA mg^?1_Pt, better that those of commercial Pt/C (340 mA mg^?1_Pt) and Pt/CNTs (162 mA mg^?1_Pt). The Pt‐WN/CNTs‐G also displayed good CO tolerance. In contrast, Pt‐WN/CNTs prepared without the grinding process displayed an activity of 344 mA mg^?1_Pt, verifying the key role of grinding treatment in the preparation of WN/CNTs with good co‐catalytic effect.     

Hierarchical Ni−Al hydrotalcite supported Pt catalyst for efficient catalytic oxidation of formaldehyde at room temperature

Catalytic oxidation at room temperature is recognized as the most promising method for formaldehyde (HCHO) removal. Pt-based catalysts are the optimal catalyst for HCHO decomposition at room temperature. Herein, flower-like hierarchical Pt/NiAl-LDHs catalysts with different [Ni²⁺]/[Al³⁺] molar ratios were synthesized via hydrothermal method followed by NaBH₄ reduction of Pt precursor at room temperature. The flower-like hierarchical Pt/NiAl-LDHs were composed of interlaced nanoplates and metallic Pt nanoparticles (NPs) approximately 3–4 nm in diameter were loaded on the surface of the Pt/NiAl-LDHs with high dispersion. The as-prepared Pt/NiAl21 nanocomposite was highly efficient in catalyzing oxidation of HCHO into CO₂ at room temperature. The high activity of the hierarchical Pt/NiAl21 nanocomposite was maintained after seven recycle tests, suggesting the high stability of the catalyst. Based on in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies, a reaction mechanism was put forward about HCHO decomposition at room temperature. This work provides new insights into designing and fabricating high-performance catalysts for efficient indoor air purification.     

Direct Observation of Dynamic Bond Evolution in Single‐Atom Pt/C3N4 Catalysts

Single‐atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single‐atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single‐atom Pt/C₃N₄ catalyst in photocatalytic water splitting by synchronous illumination X‐ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt?N bond cleavage to form a Pt⁰ species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum‐decorated C₃N₄ catalyst. As expected, H₂ production activity (14.7 mmol h^?1 g^?1) was enhanced significantly with the single‐atom Pt/C₃N₄ catalyst as compared to metallic Pt‐C₃N₄ (0.74 mmol h^?1 g^?1).     

Electrodeposition of Three‐Dimensional Porous Platinum Film on Removable Polyaniline Template for High‐Performance Electroanalysis

Three‐dimensional porous platinum (Pt_por) films are prepared based on Pt electrodeposition on polyaniline (PANI) modified electrodes followed by selective dissolution of PANI with HNO₃. Electrochemical quartz crystal microbalance data suggest that the PANI‐H₂PtCl₆ interaction involves redox and coordination reactions, depending on the working potential. The Pt_por shows better electrocatalytic performance than the Pt/PANI and conventionally electrodeposited Pt. The Pt_por modified glassy carbon electrode (GCE) can electrocatalyze the oxidation of H₂O₂ with a sensitivity of 414 µA cm^?2 mM^?1 and a detection limit of 9 nM, and the chitosan‐glucose oxidase/Pt_por/GCE can sense glucose with a sensitivity of 93.4 µA cm^?2 mM^?1.     

Preparation and characterization of Pt/C catalysts for PEMFC cathode: effect of different reduction methods

Three Pt/C catalysts for PEMFC cathode were prepared by impregnation-reduction method using HCHO, NaBH₄, and N₂H₄ as reductant, respectively, and characterized by BET, CV and XRD. The effect of reduction methods on the activity of catalysts was investigated. Compared with NaBH₄ and N₂H₄, HCHO is the most suitable one among the three reductants. The catalytic activity for oxygen reduction is in the order Pt(HCHO) > Pt(NaBH₄) > Pt(N₂H₄). This revised version was published online in June 2006 with corrections to the Cover Date.     

Pt2II and Pt2III dimers containing a Pt2(2,2′‐bipyridine)2(μ‐N,N‐dimethyl­guanidinato)2 unit

The syntheses and crystal structures of the title Pt₂^II and Pt₂^III dimers doubly bridged with N,N‐dimethyl­guanidinate ligands, namely bis­(μ‐N,N‐dimethyl­guanidinato)bis­[(2,2′‐bipyridine)platinum(II)](Pt—Pt) bis­(hexa­fluoro­phosphate) acetonitrile disolvate, [Pt₂^II(C₃H₈N₃)₂(C₁₀H₈N₂)₂](PF₆)₂·2CH₃CN, (I), and guanidinium bis­(μ‐N,N‐dimethyl­guanidinato)bis­[(2,2′‐bipyridine)sulfatoplatinum(III)](Pt—Pt) bis­(hexa­fluoro­phosphate) nitrate hexa­hydrate, (C₃H₁₀N₃)[Pt^III₂(C₃H₈N₃)₂(SO₄)₂(C₁₀H₈N₂)₂]NO₃·6H₂O, (II), are reported. The oxidation of the Pt₂^II dimer into the Pt₂^III dimer results in a marked shortening of the Pt—Pt distance from 2.8512 (6) to 2.5656 (4) Å. The change is mainly compensated for by the change in the dihedral angle between the two Pt coordination planes upon oxidation, from 21.9 (2) to 16.9 (3)°. We attribute the relatively strong one‐dimensional stack of dimers achieved in the Pt₂^II compound in part to the strong Pt^II⋯C(bpy) associations (bpy is 2,2′‐bipyridine) in the crystal structure [Pt⋯C = 3.416 (10) and 3.361 (12) Å].     

甲醛还原Pt/TiO2催化剂用于温和条件下高效催化氧化甲醛

通过浸渍法(IM)和沉积-沉淀(DP)法制备了一系列Pt/TiO2(P25)催化剂,并分别用甲醛溶液和氢气还原处理催化剂.利用原位红外监测催化剂表面吸附物种在反应过程中的变化,探究了催化剂制备和还原条件及Pt负载量对催化剂结构和催化氧化甲醛活性的影响.结果显示,用DP法制备并用甲醛还原的Pt/P25催化剂中Pt颗粒分散均匀,并具有合适的粒径和高浓度的表面活性氧,显示出良好的甲醛氧化活性.在空速30000 ml/(g·h)、反应温度30°C和甲醛初始浓度50 mg/m3的条件下,0.4%Pt/P25(DP-HCHO)上的甲醛转化率达到98%,并能稳定运行100 h以上.相比之下, Pt/P25(DP-H2)由于表面活性氧较少,不利于甲酸盐氧化,活性较低. Pt/P25(IM-H2)虽然具有高浓度的表面活性氧,却同时具有最大的Pt颗粒粒径,在甲醛转化为甲酸盐和甲酸盐氧化两步反应中的活性均较差,因而甲醛氧化活性最差.     

A one‐dimensional chloride‐bridged PtII/PtIV mixed‐valence complex with a 4‐[(4‐hydroxyphenyl)diazenyl]benzenesulfonate counter‐ion

The title compound, catena‐poly[[[bis(ethylenediamine‐κ²N,N′)platinum(II)]‐ μ‐chlorido‐[bis(ethylenediamine)platinum(IV)]‐μ‐chlorido] tetrakis{4‐[(4‐hydroxyphenyl)diazenyl]benzenesulfonate} dihydrate], {[Pt^IIPt^IVCl₂(C₂H₈N₂)₄](HOC₆H₄N=NC₆H₄SO₃)₄·2H₂O}_n, has a linear chain structure composed of square‐planar [Pt(en)₂]²⁺ (en is ethylenediamine) and elongated octahedral trans‐[PtCl₂(en)₂]²⁺ cations stacked alternately, bridged by Cl atoms, along the b axis. The Pt atoms are located on an inversion centre, while the Cl atoms are disordered over two sites and form a zigzag ...Cl—Pt^IV—Cl...Pt^II... chain, with a Pt^IV—Cl bond length of 2.3140 (14) Å, an interatomic Pt^II...Cl distance of 3.5969 (15) Å and a Pt^IV—Cl...Pt^II angle of 170.66 (6)°. The structural parameter indicating the mixed‐valence state of the Pt atom, expressed by δ = (Pt^IV—Cl)/(Pt^II...Cl), is 0.643.     

Accelerating Oxygen‐Reduction Catalysts through Preventing Poisoning with Non‐Reactive Species by Using Hydrophobic Ionic Liquids

Developing cost‐effective electrocatalysts for the oxygen reduction reaction (ORR) is a prerequisite for broad market penetration of low‐temperature fuel cells. A major barrier stems from the poisoning of surface sites by nonreactive oxygenated species and the sluggish ORR kinetics on the Pt catalysts. Herein we report a facile approach to accelerating ORR kinetics by using a hydrophobic ionic liquid (IL), which protects Pt sites from surface oxidation, making the IL‐modified Pt intrinsically more active than its unmodified counterpart. The mass activity of the catalyst is increased by three times to 1.01 A mg^?1_Pt@0.9 V, representing a new record for pure Pt catalysts. The enhanced performance of the IL‐modified catalyst can be stabilized after 30 000 cycles. We anticipate these results will form the basis for an unprecedented perspective in the development of high‐performing electrocatalysts for fuel‐cell applications.     

组合型Pt/TiO_2催化剂用于低温催化甲苯完全氧化

将均匀分布的纳米Pt粒子直接吸附到TiO2载体上,即制得了组合型Pt/TiO2催化剂(Pt/TiO2-AS).与浸渍法制备的Pt/TiO2催化剂(Pt/TiO2-WI)比较,Pt/TiO2-AS催化剂在催化甲苯完全氧化反应中表现出了很好的催化性能,甲苯转化率为100%时的反应温度低至150°C,而且即使在较高甲苯浓度和较高气体空速下,该催化剂也能保持较好的催化性能.通过X射线衍射(XRD)、N2吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)及傅里叶变换红外(FTIR)光谱等对两种Pt/TiO2催化剂的结构和表面性能进行了表征.结果表明组合型Pt/TiO2-AS催化剂粒径小(2.5 nm),活性组分主要以Pt0形式存在且分布在载体表面,而且载体表面Ti―O键活化使催化剂具有较强的催化氧化能力.另外,活性中心的价态变化(Pt0→Ptδ+)是导致Pt/TiO2-AS催化剂失活的主要原因.     

Di‐μ‐pivalamidato‐κ4N:O;O:N‐bis­[(2,2′‐bi­pyridine‐κ2N,N′)(sulfato‐κO)­platinum(III)] tetrahydrate in a head‐to‐tail isomerism

The title compound, [Pt₂^III(C₅H₁₀NO)₂(SO₄)₂(C₁₀H₈N₂)₂]·4H₂O, is the first reported example of a complex in which an amidate‐bridged Pt(bpy) dimer is stabilized in the oxidation level of Pt^III (bpy is 2,2′‐bi­pyridine). The asymmetric unit consists of one half of the formula unit with a twofold axis passing through the center of the dimer. The intradimer Pt^III—Pt^III bond distance [2.5664 (6) Å] is comparable to those reported for α‐pyridonate‐bridged cis‐diammineplatinum(III) dimers [2.5401 (5)–2.5468 (8) Å; Hollis & Lippard (1983). Inorg. Chem. 22 , 2605–2614], in spite of the close contact between the bpy planes within the dimeric unit. The axial Pt—O_sulfate distance is 2.144 (7) Å.     

A one‐dimensional iodine‐bridged PtII/PtIV mixed‐valence complex,catena‐poly[[[bis­(ethyl­ene­diamine)­platinum(II)]‐μ‐iodo‐[bis­(ethyl­ene­di­amine)platinum(IV)]‐μ‐iodo] hydrogenphosphate dihydrogenphosphate iodide trihydrate]

The title compound, {[Pt^IIPt^IVI₂(C₂H₈N₂)₄](HPO₄)(H₂PO₄)I·3H₂O}_n, has a chain structure composed of square‐planar [Pt(en)₂]²⁺ and elongated octa­hedral trans‐[PtI₂(en)₂]²⁺ cations (en is ethyl­ene­diamine) stacked alternately along the c axis and bridged by the I atoms; a three‐dimensionally valence‐ordered system exists with respect to the Pt sites. The title compound also has a unique cyclic tetra­mer structure composed of two hydrogenphosphate and two dihydrogenphosphate ions connected by strong hydrogen bonds [O⋯O = 2.522 (10), 2.567 (10) and 2.569 (11) Å]. The Pt and I atoms form a zigzag ⋯I—Pt^IV—I⋯Pt^II⋯ chain, with Pt^IV—I bond distances of 2.6997 (7) and 2.6921 (7) Å, inter­atomic Pt^II⋯I distances of 3.3239 (8) and 3.2902 (7) Å, and Pt^IV—I⋯Pt^II angles of 154.52 (3) and 163.64 (3)°. The structural parameters indicating the mixed‐valence state of platinum, expressed by δ = (Pt^IV—I)/(Pt^II—I), are 0.812 and 0.818 for the two independent I atoms.     

Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Complete dehydrogenation of methane is studied on model Pt catalysts by means of state‐of‐the‐art DFT methods and by a combination of supersonic molecular beams with high‐resolution photoelectron spectroscopy. The DFT results predict that intermediate species like CH₃ and CH₂ are specially stabilized at sites located at particles edges and corners by an amount of 50–80 kJ mol^?1. This stabilization is caused by an enhanced activity of low‐coordinated sites accompanied by their special flexibility to accommodate adsorbates. The kinetics of the complete dehydrogenation of methane is substantially modified according to the reaction energy profiles when switching from Pt(111) extended surfaces to Pt nanoparticles. The CH₃ and CH₂ formation steps are endothermic on Pt(111) but markedly exothermic on Pt₇₉. An important decrease of the reaction barriers is observed in the latter case with values of approximately 60 kJ mol^?1 for first C? H bond scission and 40 kJ mol^?1 for methyl decomposition. DFT predictions are experimentally confirmed by methane decomposition on Pt nanoparticles supported on an ordered CeO₂ film on Cu(111). It is shown that CH₃ generated on the Pt nanoparticles undergoes spontaneous dehydrogenation at 100 K. This is in sharp contrast to previous results on Pt single‐crystal surfaces in which CH₃ was stable up to much higher temperatures. This result underlines the critical role of particle edge sites in methane activation and dehydrogenation.     

Ethylene Glycol Electrooxidation Based on Pentangle‐Like PtCu Nanocatalysts

The research of active and stable electrocatalysts toward liquid‐fuel oxidation reaction is of great significance for the large‐scale commercialization of fuel cells. Although extensive efforts have been devoted to pursuing high‐performance nanocatalysts for fuel cells, both the high cost and sluggish reaction kinetics have been two major drawbacks that limited its commercial development. In this regard, we demonstrated a facile solvothermal method for the syntheses of an advanced class of PtCu nanocatalysts with a unique pentangle‐like shape. By combining the merits of a highly active surface area as well as the synergistic and electronic effects, the as‐prepared pentangle‐like Pt₃Cu nanocatalysts showed superior electrocatalytic activity towards ethylene glycol oxidation with a mass and specific activities of 5162.6 mA mg^?1 and 9.7 mA cm^?2, approximately 5.0 and 5.1 times higher than the commercial Pt/C, respectively. More significantly, the Pt₃Cu pentangle also showed excellent long‐term stability with less activity decay and negligible changes in structure after 500 cycles, indicating another class of anode catalysts for fuel cells and beyond.     

Carbon‐Supported Divacancy‐Anchored Platinum Single‐Atom Electrocatalysts with Superhigh Pt Utilization for the Oxygen Reduction Reaction

Maximizing the platinum utilization in electrocatalysts toward oxygen reduction reaction (ORR) is very desirable for large‐scale sustainable application of Pt in energy systems. A cost‐effective carbon‐supported carbon‐defect‐anchored platinum single‐atom electrocatalysts (Pt₁/C) with remarkable ORR performance is reported. An acidic H₂/O₂ single cell with Pt₁/C as cathode delivers a maximum power density of 520 mW cm^?2 at 80 °C, corresponding to a superhigh platinum utilization of 0.09 g_Pt kW^?1. Further physical characterization and density functional theory computations reveal that single Pt atoms anchored stably by four carbon atoms in carbon divacancies (Pt‐C₄) are the main active centers for the observed high ORR performance.     

Highly Oxidized Platinum Nanoparticles Prepared through Radio‐Frequency Sputtering: Thermal Stability and Reaction Probability towards CO

Platinum‐oxide nanoparticles were prepared through the radio‐frequency (RF) discharge sputtering of a Pt electrode in an oxygen atmosphere. The structure, particles size, electronic properties, and surface composition of the RF‐sputtered particles were studied by using transmission electron microscopy and X‐ray photoelectron spectroscopy. The application of the RF discharge method resulted in the formation of highly oxidized Pt⁴⁺ species that were stable under ultrahigh vacuum conditions up to 100 °C, indicating the capability of Pt⁴⁺–O species to play an important role in the oxidation catalysis under real conditions. The thermal stability and reaction probability of Pt⁴⁺ oxide species were analyzed and compared with those of Pt²⁺ species. The reaction probability of PtO₂ nanoparticles at 90 °C was found to be about ten times higher than that of PtO‐like structures.     

Complete and Rapid Conversion of Hydrazine Monohydrate to Hydrogen over Supported Ni–Pt Nanoparticles on Mesoporous Ceria for Chemical Hydrogen Storage

The development of active, selective, and robust catalysts is a key issue in promoting the practical application of hydrazine monohydrate (N₂H₄ ? H₂O) as a viable hydrogen carrier. Herein, the synthesis of a supported Ni–Pt bimetallic nanocatalyst on mesoporous ceria by a one‐pot evaporation‐induced self‐assembly method is reported. The catalyst exhibits exceptionally high catalytic activity, 100 % selectivity, and satisfactory stability in promoting H₂ generation from an alkaline solution of N₂H₄ ? H₂O at moderate temperatures. For example, the Ni₆₀Pt₄₀/CeO₂ catalyst enabled complete decomposition of N₂H₄ ? H₂O to generate H₂ at a rate of 293 h^?1 at 30 °C in the presence of 2 M NaOH, which compares favorably with the reported N₂H₄ ? H₂O decomposition catalysts. Phase/structural analysis by XRD, TEM, and Auger electron spectroscopy was conducted to gain insight into the excellent catalytic performance of the Ni–Pt/CeO₂ catalyst.     

Platinum‐Containing Polyoxometalates: syn‐ and anti‐[PtII2(α‐PW11O39)2]10− and Formation of the Metal–Metal‐Bonded di‐PtIII Derivatives

The first examples of dimeric, di‐Pt^II‐containing heteropolytungstates are reported. The two isomeric di‐platinum(II)‐containing 22‐tungsto‐2‐phosphates [anti‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 1 a ) and [syn‐Pt^II₂(α‐PW₁₁O₃₉)₂]^10? ( 2 a ) were synthesized in aqueous pH 3.5 medium using one‐pot procedures. Polyanions 1 a and 2 a contain a core comprising two face‐on PtO₄ units, with a Pt???Pt distance of 2.9–3 Å. Both polyanions were investigated by single‐crystal XRD, IR, TGA, UV/Vis, ³¹P NMR, ESI‐MS, CID‐MS/MS, electrochemistry, and DFT. On the basis of DFT and electrochemistry, we demonstrated that the {Pt₂^II} moiety in 1 a and 2 a can undergo fully reversible two‐electron oxidation to {Pt₂^III}, accompanied by formation of a single Pt?Pt bond. Hence we have discovered the novel subclass of Pt^III‐containing heteropolytungstates.     

Carbon-supported IrSn catalysts for a direct ethanol fuel cell

Carbon-supported Ir₃Sn/C and Ir/C catalysts were simply prepared with NaBH₄ as a reducing agent under the protection of ethylene glycol at room temperature. TEM and X-ray diffraction (XRD) data showed that the catalysts with small particle size exhibited the typical characteristic of a crystalline Ir fcc structure. Their electro-catalytic activities in comparison with Pt/C and Pt₃Sn/C catalysts also prepared by the NaBH₄ reduction process were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) techniques. The results indicated that Ir-based catalysts showed superior electro-catalytic activity towards ethanol oxidation to Pt/C and Pt₃Sn/C catalysts, mainly at low potential region. During single-cell tests at 90 °C, better performances of Ir-based catalysts as anodes were obtained compared to that of Pt/C catalyst. The comparable overall performance of Ir₃Sn/C to Pt₃Sn/C makes it a promising alternative choice of anode catalyst for direct ethanol fuel cells.     

Catalytic oxidation of volatile organic compounds (VOCs). Oxidation of o-xylene over Pd and Pt/HFAU catalysts

The transformation of o-xylene in low concentration (1 700 ppmv) into air was investigated over Pd and Pt/HFAU catalysts (framework Si/Al ratio equal to 17 and 100). Whatever the catalyst, o-xylene oxidation into CO₂ and H₂O is accompanied by the retention within the zeolite pores of heavy compounds (‘coke’). The relative significance of these reactions depends on the operating conditions (temperature, time-on-stream) and on the catalyst characteristics (Pd or Pt, Si/Al ratio). Over Pt and Pd/HFAU(17), time-on-stream has a positive effect on the xylene oxidation apparently related to the reducibility of Pd and Pt species during the reaction. The higher activity of Pt/HFAU catalysts can be attributed to its greater number of active species (especially Pt⁰). Those active species can be more rapidly formed than Pd⁰ by auto reduction during the calcination of Pt precursor. Whatever the metal, the higher the Si/Al ratio of the support, the faster the xylene oxidation and the lower the coke formation. This can be related to the higher proportion of reduced species (Pd⁰ and Pt⁰) formed on the more dealuminated catalyst but also to the hydrophobicity of the support. Indeed, the hydrophobicity of the zeolite play a positive role in the oxidation activity in presence of steam; the higher the Si/Al ratio of the zeolite, the faster the o-xylene oxidation. Thus a catalyst with a low platinum content supported on a hydrophobic zeolite (0.10 Pt/HFAU(100)) allows to oxidising totally o-xylene at 210 °C in presence of steam.