Adsorption and Dehydration Reaction of Ethanol to Ethylene on Isomorphous B, Al, and Ga Substitution of H-ZSM-5 Zeolite: An Embedded ONIOM Study

Dehydration reactions are important in the petroleum and petrochemical industries, especially for the feedstock production. In this work, the catalytic activity of zeolites with different acidities for the dehydration of ethanol to ethylene was investigated by calculations on cluster models of three isomorphous B, Al, and Ga substitution of H-ZSM-5 zeolites. Detailed reaction profiles for the dehydration reaction, assuming either a stepwise or a concerted mechanism, were calculated by using the ONIOM(MP2:M06-2X) + SCREEP method. The adsorption energies of ethanol are -21.6, -28.1 and -27.7 kcal/mol on H-[B]-ZSM-5, H-[Al]-ZSM-5, H-[Ga]-ZSM-5 zeolites, respectively. The stepwise mechanism was preferred on all isomorphous zeolites. The activation energies for the ethoxy formation as the rate-determining step are in range of 40.0 to 42.3 kcal/mol. The results indicated that the order of catalytic activity were H-[Al]-ZSM-5 > H-[Ga]-ZSM-5 > H-[B]-ZSM-5 for catalyzing the dehydration of ethanol to ethylene. Besides the acid strength, the zeolite framework affected the reaction by stabilizing the reaction intermediates leading to more stable adsorption complexes and lower activation barriers.

Effects of Ga Substitution on Micromorphology and Static Magnetic Properties of Self-Biased M-Type Sr Hexaferrites

The Sr hexaferrites with chemical formula Sr0.4La0.3Ca0.3Fe11.85-xGaxCo0.15O19 (x = 0.0 — 1.4) were manufactured by traditional ceramic method. The affect of Ga substitution on static magnetic properties and micromorphology of M-type Sr (SrM) hexaferrites have been presented in detail. In accordance with the experiment results, as Ga-substituted content x rises up from 0.0 to 1.4, all SrM hexaferrite samples are magnetoplumbite hexagonal structure. The difference between radius of Fe3+ and Ga3+ ions leads to the decrease of lattice constants. As the amount of Ga substitution x increases from 0.0 to 1.4, the 4πMs and 4πMr presents a trend of increasing, but the Hc shows the opposite trend. K1 and Ha of all samples are higher than 2.5×105 J/m3 and 21 kOe respectively, which manifests all samples possess the strong uniaxial anisotropy. The materials discussed in this paper possess huge potential in the application of high frequency self-biased microwave devices.

Effect of Ga and Zr Substitution on the Properties of Dy2Fe17−XZrX and Dy2Fe16Ga1−xZrx (0 ≤ x ≤ 1) Intermetallic Compounds Prepared via Arc Melting Process

The effects of substitution of Zr and Ga on the structural and magnetic properties of Dy2Fe17 intermetallic compound were investigated in this study. The Rietveld analysis confirmed that the crystalline system was a Th2Ni17 structure. Lattice parameters a (Å) and c (Å), unit cell volume (Å3), and bonding distance (Å) were calculated using Rietveld analysis. The unit cell volume of Dy2Fe17−xZrx and Dy2Fe16Ga1−xZrx increased linearly with Zr and Ga substitution. The Curie temperature (Tc) of Dy2Fe17−xZrx and Dy2Fe16Ga1−xZrx was found to be Zr content-dependent. The maximum Curie temperatures were observed at 510 K (x = 0.75 Zr content) for Dy2Fe17−xZrx and 505.1 K (x = 0.5 Zr content) for Dy2Fe16Ga1−xZrx, which are 102 K and 97 K higher than the value found for Dy2Fe17, respectively. The room-temperature Mössbauer analysis showed a decrease in the average hyperfine field and increases in the isomer shift with Zr doping. The overall improvement in Curie temperature with the substitution strategy of Zr–Ga substitution in 2:17 intermetallic compounds could find potential use of these magnetic compounds in high-temperature applications.