Reversible Transformation and Distribution Determination of Diverse Pt Single-Atom Species.

In single-atom catalysts (SACs), the complexity of the support anchoring sites creates a vast diversity of single-atom species with varied coordination environments. To date, the quantitative distribution of these diverse single-atom species in a given SAC has remained elusive. Recently, CeO2-supported metal SACs have been extensively studied by modulating their local environments via numerous synthetic strategies. However, owing to the absence of a quantitative description, unraveling the site-specific reactivity and regulating their transformation remain challenging. Here, we show that two distinct Pt/CeO2 SACs can be reversibly generated by oxidative and nonoxidative dispersions, which contain varied Pt1On-Ceδ+ single-atom species despite similar Pt charge states and coordination numbers. By means of Raman spectroscopy and computational studies, we semiquantitatively reveal the distribution of diverse Pt1On-Ceδ+ species in each specific SACs. Remarkably, the minority species of Pt1O4-Ce3+-Ov accounting for only 14.2% affords the highest site-specific reactivity for low-temperature CO oxidation among the other abundant counterparts, i.e., Pt1O4-Ce4+ and Pt1O6-Ce4+. The second nearest oxygen vacancy (Ov) not only acts synergistically with the nearby active metal sites to lower the reaction barrier but also facilitates the dynamic transformation from six-coordinated to four-coordinated sites during cyclic nonoxidative and oxidative dispersions. This work elucidates the quantitative distribution and dynamic transformation of varied single-atom species in a given SAC, offering a more intrinsic descriptor and quantitative measure to depict the inhomogeneity of SACs.

Synthesis, characterization, and catalytic application of hierarchical nano-ZSM-5 zeolite.

Hierarchical nano-ZSM-5 zeolites (Z5-X) with different grain sizes were synthesized by varying amounts of 3-glycidoxypropyltrimethoxysilane (KH-560) in the hydrothermal synthesis strategy. Moreover, the conventional ZSM-5zeolite(Z5), which was prepared without KH-560, was used as the reference sample. The crystalline phases, morphologies, porous characteristics, Si/Al molar ratios and acidic properties of all fresh catalysts were characterized using the X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), N2 adsorption-desorption, inductively coupled plasma atomic emission spectroscopy (ICP) and temperature programmed desorption of ammonia (NH3-TPD) techniques. Results show that the grain size and strong acid amount of zeolite decreased with the increasing amount of KH-560. The micropore surface areas and the corresponding volume of Z5-X changed less compared with Z5. Consequently, the high shape-selectivity of zeolite was preserved well under the addition of KH-560. However, the mesopore surface areas and the corresponding volume increased significantly with the increasing amount of KH-560. Benefiting from the abundant hierarchical structure, the Z5-X catalysts exhibited a larger coke capacity than the Z5 catalyst. The coke depositions of all the deactivated catalysts were characterized by the thermogravimetric technique (TG), and the results are indicative of the decreased average rate of coke deposition with an increasing amount of KH-560, which could result from the gradually reduced strong acid amount and the nano-sized crystallites. The catalytic performance of methanol-to-aromatics (MTA) indicates that the Z5-0.12 catalyst exhibited higher catalytic activity and selectivity of BTX as the reaction was prolonged, which could result from the synergistic effect among the proper strong acid amount, the smaller zeolite grain size, and the abundant hierarchical structure.

Forming pure shaped ZSM-5 zeolite bodies by a steam-assisted method and their application in methanol to aromatic reactions.

For an industrial-scale catalytic process with a fixed or packed bed reactor, powder catalysts are not suitable because they may block the reaction pipe and increase the pressure of the reactor. Therefore, catalyst molding is essential for the industrial application of a catalyst. During the catalyst molding, binders are employed as indispensable additives that can achieve the mechanical strength requirements for industrial applications. However, the addition of binders may cover the activity sites of the catalyst and suppress the mass transfer of the reactants and products. So, traditional processes of catalyst molding significantly affect the catalytic performance. In this study, we proposed a vapor-phase-treatment to synthesize a pure shaped ZSM-5 zeolite with the re-crystallization of the binder incorporated silica sol and aluminum nitrate, which were converted into a part of ZSM-5 on a commercial H-ZSM-5 zeolite substrate. Subsequently, the shaped ZSM-5 catalyst was evaluated using the catalytic conversion of methanol to an aromatic (MTA reaction). The results showed that compared to the EPHZ catalyst, the SPHZ catalyst exhibited a long lifetime with a relatively high shape selectivity for methanol and aromatics. To rationalize these results and establish a structure-activity relationship, the zeolite catalysts were thoroughly characterized by XRD, NH3-TPD, FT-IR, N2 adsorption, TG, SEM, TEM, ICP and Al MAS-NMR. The results demonstrated that an interesting intra-particle pore structure was formed within the monoliths of the SPHZ catalyst. Moreover, the superior catalytic performance obtained for SPHZ may have also been due to the broad acid strength distribution and the conversion of the silicon aluminum adhesive agent to zeolite crystals.

Effect of cobalt addition on the structure and properties of Ni-MCM-41 for the partial oxidation of methane to syngas.

A one-step hydrothermal crystallization method was used to synthesize Co-Ni-MCM-41 catalysts for the partial oxidation of methane to syngas reaction. Co was added as an assistant in the synthesis process. The formation of a Ni-Co alloy decreased the damage of Ni ions to the framework of MCM-41. The Ni-Co alloy introduced more Ni into the channel exposing more active sites. The properties of the synthesized catalysts were characterized by XRD, N2 adsorption-desorption, TEM, ICP, FT-IR, H2-TPR, XPS and TGA techniques. Co-Ni-MCM-41 catalysts showed superior catalytic performance and sintering resistance than Ni-MCM-41 catalyst without Co. The Ni-Co alloy inhibited the formation of the NiO, thus reducing the sintering of the catalyst. The result was attributed to higher metal dispersion and more regular pore structure of the Co-Ni-MCM-41 catalysts. When the Co content was 1%, a conversion of 88% and selectivity of 87% was achieved.

Amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 based on dye sensitization of the semiconductor composite C3N4-MoS2.

The authors describe an amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 (CA724). The method employs a C3N4-MoS2 semiconductor as the photoelectric conversion layer. The nanocomposite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. The dye eosin Y was encapsulated into CaCO3 nanospheres which then were used as labels for antibody against CA724. In addition, Fe3O4 nanospheres were employed as magnetic platform for constructing photoelectrochemical sandwich immunoassay. The CaCO3 nanospheres can be dissolved with aid of ethylene diamine tetraacetic acid (EDTA) and the carried eosin Y in CaCO3 is released. The released dyes sensitizes the C3N4-MoS2 semiconductor, which induces photocurrent amplification. Under optimal conditions and at a typical working voltage of 0 V (vs. SCE), the photocurrent increases linearly in the range of 0.05 mU mL-1 to 500 mU mL-1 of CA724, with a 0.02 mU mL-1 detection limit. Graphical abstract The C3N4-MoS2 complex, with high efficiency of electron transport, was synthesized to construct a photoelectrochemical analytical platform. A sandwich-type immunoassay was established on the surface of magnetic beads. Carbohydrate antigen 724 in sample was detected sensitively by using sensitization of released eosin Y as signal amplifiery.

Dye sensitized photoelectrochemical immunosensor for the tumor marker CEA by using a flower-like 3D architecture prepared from graphene oxide and MoS2.

The authors describe a dye-sensitized photoelectrochemical immunoassay for the tumor marker carcinoembryonic antigen (CEA). The method employs the rhodamine dye Rh123 with red color and absorption maximum at 500 nm for spectral sensitization, and a 3D nanocomposite prepared from graphene oxide and MoS2 acting as the photoelectric conversion layer. The nanocomposite with flower-like 3D architectures was characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. A photoelectrochemical sandwich immunoassay was developed that is based on the use of the nanocomposite and based on the specific binding of antibody and antigen, and by using a secondary antibody labeled with Rh123 and CdS (Ab2-Rh123@CdS). Under optimal conditions and at a typical working voltage of 0 V (vs. Hg/HgCl2), the photocurrent increases linearly 10 pg mL-1 to 80 ng mL-1 CEA concentration range, with a 3.2 pg mL-1 detection limit. Graphical abstract Flower-like GO-MoS2 complex with high efficiency of electron transport was synthesized to construct photoelectrochemical platform. The sandwich-type immunoassay was built on this platform based on specific binding of antigen and antibody. Carcinoembryonic antigen in sample was detected sensitively by using sensitization of rhodamine dye Rh123 as signal amplification strategy.

Displacement-type amperometric immunosensing platform for sensitive determination of tumour markers.

The sensitive determination of carcino embryonie antigen (CEA)-a set of highly related glycoproteins involved in cell adhesion-is beneficial to the early diagnosis of colorectal cancer. In this study, a novel displacement-type amperometric immunosensing platform, based on the fact that glucose and Alizarin Red S (ARS) compete for phenylboronic acid bindng sites, was projected for sensitive detection of tumour marker (CEA, used as a model) on a PAMAM dendrimer-encapsulated nanogold (PAMAM-Au)-functionlized sensing interface. Firstly, 4(-)mercaptophenylboronic acid (S-PBA) was assembled onto the PAMAM-Au via the S-Au interaction, and then ARS was immobilized by S-PBA binding of cis-diol moieties, which was dropped on the surface of glassy carbon electrode as sensing platform to combine antibody. Meanwhile, amylase modified gold nanoparticles were employed as labels. Accompanying the sandwich immunoassay, the carried amylase could hydrolyze amylose into glucose, and the displacement-type format was triggered due to the stronger adhesion between glucose and PBA, which resulted in the change of electrochemical signals due to the decrease of ARS (as an electron mediator). Under optimal conditions, the SWV signals were related to the concentration of CEA, indicating a certain proportional relation in a range of 0.01~50ngmL(-1) with a detection limit (LOD) of 0.003ngmL(-1). Intra- and inter-assay coefficients of variation were below 10%, respectively. In addition, the methodology showed good accordance with a commercialized enzyme-linked immunosorbent assay (ELISA) method.