Particle Size Of Active Phase Research Articles

Structure Sensitivity of Ammonia Synthesis on Cobalt: Effect of the Cobalt Particle Size on the Activity of Promoted Cobalt Catalysts Supported on Carbon

This work presents a size effect, i.e., catalyst surface activity, as a function of active phase particle size in a cobalt catalyst for ammonia synthesis. A series of cobalt catalysts supported on carbon and doped with barium was prepared, characterized (TEM, XRPD, and H2 chemisorption), and tested in ammonia synthesis (9.0 MPa, 400 °C, H2/N2 = 3, 8.5 mol% of NH3). The active phase particle size was varied from 3 to 45 nm by changing the metal loading in the range of 4.9–67.7 wt%. The dependence of the reaction rate expressed as TOF on the active phase particle size revealed an optimal size of cobalt particles (20–30 nm), ensuring the highest activity of the cobalt catalyst in the ammonia synthesis reaction. This indicated that the ammonia synthesis reaction on cobalt is a structure-sensitive reaction. The observed effect may be attributed to changes in the crystalline structure, i.e., the appearance of the hcp Co phase for the particles with a diameter of 20–30 nm.

The Relationship between Reaction Temperature and Carbon Deposition on Nickel Catalysts Based on Al2O3, ZrO2 or SiO2 Supports during the Biogas Dry Reforming Reaction

The tackling of carbon deposition during the dry reforming of biogas (BDR) necessitates research of the surface of spent catalysts in an effort to obtain a better understanding of the effect that different carbon allotropes have on the deactivation mechanism and correlation of their formation with catalytic properties. The work presented herein provides a comparative assessment of catalytic stability in relation to carbon deposition and metal particle sintering on un-promoted Ni/Al2O3, Ni/ZrO2 and Ni/SiO2 catalysts for different reaction temperatures. The spent catalysts were examined using thermogravimetric analysis (TGA), Raman spectroscopy, high angle annular dark field scanning transmission electron microscopy (STEM-HAADF) and X-ray photoelectron spectroscopy (XPS). The results show that the formation and nature of carbonaceous deposits on catalytic surfaces (and thus catalytic stability) depend on the interplay of a number of crucial parameters such as metal support interaction, acidity/basicity characteristics, O2– lability and active phase particle size. When a catalytic system possesses only some of these beneficial characteristics, then competition with adverse effects may overshadow any potential benefits.

Direct syngas to DME as a clean fuel: The beneficial use of ultrasound for the preparation of CuO–ZnO–Al2O3/HZSM-5 nanocatalyst

A series of CuO–ZnO–Al2O3/HZSM-5 nanocatalysts prepared by impregnation, co-precipitation–physically mixing and combined co-precipitation–ultrasound methods and their catalytic activity investigated toward direct conversion of syngas to DME. BET, XRD, FESEM, TPR-H2 and FTIR techniques were used to characterize nanocatalysts. XRD and FTIR results showed that structure of HZSM-5 is not damaged even after it is loaded with CuO–ZnO–Al2O3 nanoparticles. TPR-H2 profiles indicated that reducibility of co-precipitation–ultrasound nanocatalyst is higher than other catalysts. It is found that employing ultrasound energy has great influence on the dispersion of nanocatalyst and its catalytic performance. Size distribution histogram of this nanocatalyst indicated that active phase particle size is between 25.7 and 125.4nm and their average size is 47.86nm. The physically mixing of CuO–ZnO–Al2O3 and HZSM-5 resulted in the low catalytic activity, indicating that the closest packing of both active sites for CO hydrogenation and methanol dehydration is necessary for direct synthesis of DME. The nanocatalyst loses negligible activity over the course of reaction due to coke formation on copper species.

Direct synthesis of dimethyl ether on the admixed nanocatalystsof CuO–ZnO–Al2O3 and HNO3-modified clinoptilolite at high pressures: Surface properties and catalytic performance

The potential of clinoptilolite as a methanol dehydration catalyst in direct conversion of syngas to dimethyl ether has been investigated. The modified form of clinoptilolite was obtained by nitric acid treatment. Although the physicochemical analysis showed that crystallinity of the clinoptilolite decreased during HNO3-treatment, the specific surface area of natural zeolite increased considerably. Size distribution histogram of the synthesized nanocatalyst showed that the particle size of active phase was between 28.9 and 112.9nm with an average size of 53.9nm. The NH3-TPD profiles showed that both the number and strength of the acid sites of the CuO–ZnO–Al2O3/clinoptilolite nanocatalysts decreased with increasing active phase content. Results indicated that the optimal reaction temperature and pressure for this nanocatalysts were 300°C and 40bar, respectively. The catalytic performance of synthesized samples showed that the optimum CuO–ZnO–Al2O3 to clinoptilolite ratio was 4:1, which depends on temperature and pressure.