The active sites of supported silver particle catalysts in formaldehyde oxidation

2016 ◽  
Vol 52 (65) ◽  
pp. 9996-9999 ◽  
Author(s):  
Yaxin Chen ◽  
Zhiwei Huang ◽  
Meijuan Zhou ◽  
Pingping Hu ◽  
Chengtian Du ◽  
...  

Surface silver atoms with upshifted d-orbitals are identified as the catalytically active sites in formaldehyde oxidation by correlating their activity with the number of surface silver atoms, and the degree of the d-orbital upshift governs the catalytic performance of the active sites.

2015 ◽  
Vol 14 (01n02) ◽  
pp. 1460028 ◽  
Author(s):  
Yanlei Zhao ◽  
Hua Tian ◽  
Junhui He ◽  
Qiaowen Yang

Formaldehyde is regarded as the major indoor air pollutant. Because of harmful effect on human health, its emission abatement is of significant practical interest. We report here excellent low-temperature catalytic performances of mesoporous MnO x - CeO 2 catalysts in the process of formaldehyde oxidation. These MnO x - CeO 2 catalysts were synthesized by a "nanocasting" method using SBA-15 as hard template. TEM images showed that the as-fabricated MnO x - CeO 2 composites possess well-ordered mesoporous architectures. Results of catalytic tests revealed that mesoporous MnO x - CeO 2 nanocomposites have excellent low-temperature catalytic activity for formaldehyde oxidation, the temperature for 100% formaldehyde conversion can be as low as 65°C over these noble-metal-free mesoporous catalysts. The excellent catalytic performance is attributed to their ordered mesoporous structures that expose abundant active sites to formaldehyde molecules.


RSC Advances ◽  
2017 ◽  
Vol 7 (5) ◽  
pp. 2934-2942 ◽  
Author(s):  
Xia Zhang ◽  
Tianyong Zhang ◽  
Bin Li ◽  
Guanghui Zhang ◽  
Li Hai ◽  
...  

Compared the catalytic performance of complexes 1–3, the complex 2 has the highest phenol yield (24.6%) and phenol selectivity (92%), which has the highest electron densities of the catalytically active sites.


2019 ◽  
Vol 9 (3) ◽  
pp. 811-821 ◽  
Author(s):  
Zhao-Meng Wang ◽  
Li-Juan Liu ◽  
Bo Xiang ◽  
Yue Wang ◽  
Ya-Jing Lyu ◽  
...  

The catalytic activity decreases as –(SiO)3Mo(OH)(O) > –(SiO)2Mo(O)2 > –(O)4–MoO.


2019 ◽  
Author(s):  
M. Alexander Ardagh ◽  
Manish Shetty ◽  
Anatoliy Kuznetsov ◽  
Qi Zhang ◽  
Phillip Christopher ◽  
...  

Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site is achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10<sup>-6</sup> < f < 10<sup>4</sup> Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.


Author(s):  
Parisa Sadeghpour ◽  
Mohammad Haghighi ◽  
Mehrdad Esmaeili

Aim and Objective: Effect of two different modification methods for introducing Ni into ZSM-5 framework was investigated under high temperature synthesis conditions. The nickel successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. Materials and Methods: A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM-5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BET-BJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPDNH3) were applied to investigate the physicochemical properties. Results: Although all the catalysts showed pure silica MFI–type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm3 /gcat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. Conclusion: The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.


2020 ◽  
Vol 16 ◽  
Author(s):  
Anping Wang ◽  
Heng Zhang ◽  
Hu Li ◽  
Song Yang

Background: With the gradual decrease of fossil energy, the development of alternatives to fossil energy has attracted more and more attention. Biodiesel is considered to be the most potent alternative to fossil energy, mainly due to its green, renewable and biodegradable advantages. The stable, efficient and reusable catalysts are undoubtedly the most critical in the preparation of biodiesel. Among them, nanoporous carbon-based acidic materials are very important biodiesel catalysts. Objective: The latest advances of acidic nanoporous carbon catalysts in biodiesel production was reviewed. Methods: Biodiesel is mainly synthesized by esterification and transesterification. Due to the important role of nanoporous carbon-based acidic materials in the catalytic preparation of biodiesel, we focused on the synthesis, physical and chemical properties, catalytic performance and reusability. Results: Acidic catalytic materials have a good catalytic performance for high acid value feedstocks. However, the preparation of biodiesel with acid catalyst requires relatively strict reaction conditions. The application of nanoporous acidic carbon-based materials, due to the support of carbon-based framework, makes the catalyst have good stability and unique pore structure, accelerates the reaction mass transfer speed and accelerates the reaction. Conclusion: Nanoporous carbon-based acidic catalysts have the advantages of suitable pore structure, high active sites, and high stability. In order to make these catalytic processes more efficient, environmentally friendly and low cost, it is an important research direction for the future biodiesel catalysts to develop new catalytic materials with high specific surface area, suitable pore size, high acid density, and excellent performance.


2021 ◽  
Author(s):  
Hongling Yang ◽  
Xun Zhang ◽  
Yi Yu ◽  
Zheng Chen ◽  
Qinggang Liu ◽  
...  

Single-atom catalysts provide a pathway to elucidate the nature of catalytically active sites. However, keeping them stabilized during operation proves to be challenging. Herein, we employ cryptomelane-type octahedral molecular sieve...


Nanomaterials ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 1259
Author(s):  
Ana Franco ◽  
Rafael Luque ◽  
Carolina Carrillo-Carrión

Biomass-derived materials are put forward as eco-friendly alternatives to design heterogeneous catalysts. To contribute in this field, we explored the potential of mesoporous biogenic silica (RH-Silica) obtained from lignocellulosic waste, in particular from rice husk, as an inorganic support to prepare heterogenized iron oxide-based catalysts. Mechanochemistry, considered as a green and sustainable technique, was employed to synthetize iron oxide nanoparticles in pure hematite phase onto the biosilica (α-Fe2O3/RH-Silica), making this material a good candidate to perform catalyzed organic reactions. The obtained material was characterized by different techniques, and its catalytic activity was tested in the selective oxidation of styrene under microwave irradiation. α-Fe2O3/RH-Silica displayed a good catalytic performance, achieving a conversion of 45% under optimized conditions, and more importantly, with a total selectivity to benzaldehyde. Furthermore, a good reusability was achieved without decreasing its activity after multiple catalytic cycles. This work represents a good example of using sustainable approaches and green materials as alternatives to conventional methods in the production of high-added value products.


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