Full Metal Species Quantification of Metal Supported Catalysts Through Massive TEM Images Recognition

For a practical high-loading single-atom catalyst,it is prone to forming diverse metal species owing to either the synthesis inhomogeneity or the reaction induced aggregation.The diversity of this metal species challenges the discerning about the contributions of specific metal species to the catalytic performance,and thus hampers the rational catalyst design.In this paper,a distinct solution of dispersion analysis based on transmission electron microscopy imaging specialized for metal-supported catalysts has been proposed in the capability of full-metal-species quantification(FMSQ)from single atoms to nanoparticles,including dispersion densities,shape geometry,and crystallographic surface exposure.This solution integrates two image-recognition algorithms including the electron microscopy-based atom recognition statistics(EMARS)for single atoms and U-Net type deep learning network for nanoparticles in different shapes.When applied to the C_(3)N_(4)-and nitrogen-doped carbon-supported catalysts,the FMSQ method successfully identifies the specific activity contributions of Au single atoms and particles in butadiene hydrogenation,which presents remarkable variation with the metal species constitution.This work demonstrates a promising value of our FMSQ strategy for identifying the activity origin of heterogeneous catalysis.

Activation of Carbon Dioxide by Gas-phase Metal Species

Catalytic conversion of carbon dioxide(CO_(2)) into value-added chemicals is an important and active field in both of the condensed-phase and gas-phase studies. This mini-review summarizes a variety of experimentally identified reactions in the activation and transformation of CO_(2) by metal species in the gas phase. The use of advanced mass spectrometric instrumentation in conjunction with quantum chemistry calculations can uncover the mechanistic details and determine the vital factors that control the activation of CO_(2). This review focuses mainly on three topics: the activation of CO_(2) by(1) bare metal ions and metal oxide species,(2) metal hydrides, and(3) other gas-phase metal species. Emphasis is placed on the latest advances in the hydrogenation of CO_(2) mediated with metal hydrides. A potential prospect toward the future effort in the activation and transformation of CO_(2) in gas phase has also been discussed.

Effect of SiO_(2)on loss of catalysis of inherent metallic species in CO_(2)gasification of coke from lignite

Inherent metallic species retained by coal char or coke,such as Na and Ca,behave as catalysts in gasification.The char/coke normally contains inherent SiO_(2),which can react with the inherent catalysts to form silicates,resulting in catalyst deactivation over the range of pyrolysis,carbonization and gasification,and thereby reducing the char/coke reactivity.The present authors simulated the inherent catalyst deactivation experimentally by blending a Victorian lignite with SiO_(2),briquetting the SiO_(2)/lignite blend,carbonizing the briquette,and then gasifying the coke with CO_(2).The kinetic analysis of the gasification employed a comprehensive model,which assumed progress in parallel of non-catalytic and catalytic gasification.The model quantitatively described the measured kinetics of the coke gasification with different SiO_(2)contents over a range of coke conversion up to 99.9%.The kinetic analysis revealed that the SiO_(2)deactivated substantial and entire portions of the most active catalyst and its precursor,respectively,before the gasification(i.e.,during the carbonization).The catalyst deactivation also occurred during the gasification,but mainly following a self-deactivation mechanism that involved no silicates formation.

Heterogeneous Catalysis with Metal-Containing Crystalline Porous Materials:Element-and Site-Specific Insights

Metal-containing crystalline porous materials(CPMs)are gaining popularity in heterogeneous catalysis because of their highly crystalline and porous systems,and their excellent chemical tunability.Modification of the metal species and framework structure permits them to have greater activity,selectivity,and stability over other materials.An in-depth understanding of the complex nature of metal active sites in CPMs is essential for revealing the structure-performance relationships and directing the rational design of such catalysts.Compared to conventional characterization techniques,the rapid development of X-ray absorption spectroscopy(XAS)has provided element-and site-specific deep insights into the electronic and structural information of metal species in CPMs.As such,this review begins by summarizing novel XAS techniques and analysis methods in accurately obtaining such data.Next,the combination of XAS with other high-level characterization methods into disclosing the configuration of active sites in metalcontaining CPMs is presented.Then,the utilization of theory-assisted XAS data analysis in examining complex metal-containing CPM catalysts is discussed.Afterwards,advanced in-situ/operando XAS studies into revealing the working sites in metal-containing CPMs under catalytic conditions are highlighted.We conclude by outlining the future challenges and prospects of XAS measurements,data analyses,and in-situ/operando setups in advancing the study of metal-in-CPM catalysts.

The speciation, leachability and bioaccessibility of Cu and Zn in animal manure-derived biochar： effect of feedstock and pyrolysis temperature

Biochars derived from animal manures may accumulate potentially toxic metals and cause a potential risk to ecosystem. The synchrotron-based X-ray spectroscopy, sequential fractionation schemes, bioaccessibility extraction and leaching procedure were performed on poultry and swine manure-derived biochars （denoted PB and SB, respectively） to evaluate the variance of speciation and activity of Cu and Zn as affected by the feedstock and pyrolysis temperature. The results showed that Cu speciation was dependent on the feedstock with Cu-citrate-like in swine manure and species resembling Cu-glutathione and CuO in poultry manure. Pyrolyzed products, however, had similar Cu speciation mainly with species resembling Cu-citrate, CuO and CuS/Cu2S. Organic bound Zn and Zn3（PO4）2-1ike species were dominant in both feedstock and biochars. Both Cu and Zn leaching with synthetic precipitation leaching procedure （SPLP） and toxicity characteristic leaching procedure （TCLP） decreased greatly with the rise of pyrolysis temperature, which were consistent with the sequential extraction results that pyrolysis converted Cu and Zn into less labile phases such as organic/ sulfide and residual fractions. The potential bioaccessibility of Zn decreased for both the PB and SB, closely depending on the content of non-residual Zn. The bioaccessibility of Cu, however, increased for the SB prepared at 300℃ 700℃, probably due to the increased proportion of CuO. Concerning the results of sequential fi＇actionation schemes, bioaccessibility extraction and leaching procedure, pyrolysis at 500℃ was suggested as means of reducing Cu/Zn lability and poultry manure was more suitable for pyrolysis treatment.