Non-oxidative Decomposition of CH4 Over CeO2 and CeO2–SiO2 Supported Bimetallic Ni–Mo Catalysts

Catalysis Letters - The development of highly active and durable catalysts for H2 production through CH4 decomposition process is still a great challenge. In this study, CeO2 and CeO2–SiO2...     

Synthesize and characterization of new polymeric surfactants based on nonionic maleate surfmer by catalytic bulk copolymerization with methyl methacrylate

Non-ionic maleate surfmer (M1) was prepared via ring opening reaction of maleic anhydride with hexanol followed by esterfaction with polyethylene glycol. The prepared surfmer was homo-polymerized and copolymerized with methyl methacrylate (M2) at different conditions using TiO₂ and V₂O₅ as catalysts in presence of O₂ or N₂. The chemical structure of the prepared surfmer, homo-polymer and copolymer were confirmed by FT-IR, ¹³C and ¹H NMR. The molecular weights of the prepared polymers were measured using Gel Permeation Chromatography (GPC) and their thermal gravimetric analysis (TGA) was determined. TGA indicated a higher thermal stability for the copolymers M1M2TN and M1M2VO relative to the pure polymethylmethacrylate (PMMA). The interfacial tension for the prepared surfmer and the copolymer was measured. The optimum conditions which resulted in 64.2% and 63.8% conversion were 20% w/w TiO₂ in N₂ and 10% w/w V₂O₅ in O₂ at 80?°C for 4?h with M1/M2 molar ratio of 1:1.     

Performance of ultrasonic – Treated nano-zeolites employed in the preparation of dimethyl ether

Catalytic dehydration of methanol to dimethyl ether was carried out over nano-zeolites and their modified samples via ultrasonic technique. Parent H-Beta and Parent H-Mordenite zeolites are used as synthesized and after sonication. H-Mordenite sonicated for 20 and 120 min whereas H-Beta sonicated for 20 min only. The reaction temperature was varied between 100 and 225 °C at three different contact times. The different catalyst samples were characterized using: XRD, FTIR, TEM, SEM and NH₃-TPD techniques. The results revealed that sonication of parent zeolite samples affects on the unit cell dimensions and their crystal size. FTIR-spectroscopic analysis indicated that sonication may decrease the pore opening and cause framework structure defects. TEM and SEM micrographs showed that sonication broke-up and re-ordered zeolite crystals with longer time resulted in a different morphology relative to parents and also change the particle size. Sonicated samples have a good performance in methanol dehydration with complete conversion and complete selectivity to dimethyl ether at lower temperature relative to the corresponding parent zeolites. TPD results indicated that the concentration of strong acid sites decreased in sonicated H-Mordenite samples leading to an increase of their catalytic activity and the selectivity to DME. On the other hand, ultrasonic treatment of H-Beta sample decreased its catalytic activity.     

Laser induced structural and transport properties change in Cu–Zn ferrites

The samples were prepared from analar oxides (BDH) using the standard double sintering ceramic technique. X-ray diffraction (XRD) was carried out to assure the formation of the sample in single spinel phase. The effect of Q-switched Nd:YAG laser irradiation with wavelength of 1064 nm on the electrical properties of the prepared samples Cu_{1 − x} Zn _x Fe₂O₄ (0.1 ≤ x ≤ 0.6) was discussed. The temperature dependence of the polarization and a.c. conductivity was studied in the range (300 K ≤ T ≤ 700 K) at different applied frequencies (10 kHz ≤ f ≤ 4 MHz). The activation energies were calculated at different temperature regions for the unirradiated and irradiated samples. Their values indicate the semi-conducting like behaviour of the sample. Comparison between the ac electrical conductivity, dielectric constant, dielectric loss, for unirradiated and irradiated samples with different Zn concentrations (0.1 ≤ x ≤ 0.6) was performed. Seebeck voltage measurements showed that, the n and p-type conduction act in cooperation with each other. The change in a.c. conductivity is attributed to the creation of lattice vacancies after laser irradiation. The decrease of the a.c. conductivity and the dielectric constant after laser irradiation with 18000 shots may be due to formation of traps, which decrease the number of carriers. The lattice mismatch in the grain boundaries causes a planar array of localized states, being able to capture free carriers. The accumulated charge constitutes an electrostatic barrier impeding carriers from free motion. Thus, it is possible to optimize the conductivity of this type of ferrite material to be used in technological applications at room temperature.     

Effect of hydrochlorination and hydrofluorination of Pt/H-ZSM-5 and Pt–Ir/H-ZSM-5 catalysts for n-hexane hydroconversion

Pt/H-ZSM-5 and Pt–Ir/H-ZSM-5 catalysts were hydrochlorinated or hydrofluorinated with 3.0 wt%HCl or HF, respectively. These mono- and bimetallic catalysts were tested for n-hexane hydroconversion in a pulsed microcatalytic reactor in a flow of H₂ gas. The catalysts were characterized via XRD, metal dispersion via H₂ chemisorption and acid site strength distribution using temperature programmed desorption of ammonia (TPD). Although metallic promoters frequently cause inhibition of the catalytic activities of Pt and since iridium is less active than platinum, fortunately, Ir was found to enhance the hydroconversion activities of the current catalysts, particularly after hydrochlorination.     

Interaction characteristics controlling catalytic performances of Ni (II) and Cu (II) phthalocyanines immobilized on bentonite clay surface in redox-initiated polymerization of methyl methacrylate in aqueous medium

Different catalytic performances have been shown for nickel (II) phthalocyanine (1.8 wt%)/bentonite/HSO₃ ^? and copper (II) phthalocyanine (1.8 wt%)/bentonite/HSO₃ ^? initiating systems in the early stage of methyl methacrylate polymerization in aqueous medium, in the temperature range, 40–60 °C. Redox–free radical mechanisms, suggesting dual-site initiation in presence of nickel phthalocyanine system and single-site initiation by using copper phthalocyanine system, were discussed in view of different interaction and dispersion profiles of the immobilized complex systems. Both complexes exhibited strong interaction with bentonite, assisted by n-butyl amine solvent, during the immobilization process. This amine could modify bentonite surface through eliminating its narrower pores, expanding its sheet structure and using up its strongest Brönsted acid sites. Nickel phthalocyanine molecules, intercalated into bentonite clay galleries by n-butyl amine, could be located parallel to silicate layer planes in an even distribution and higher dispersion. Cation exchange or substitution mechanism involving stronger interaction between Ni²⁺ ions and Al³⁺ sites in the octahedral sheet encouraged dual-site initiation; two active Ni sites, accessible from one side each, coordinated with two monomer molecules. Copper phthalocyanine molecules, drawn in an inclined edge-on orientation, displayed a strong interaction between N’s of the macro-ring system and the clay external edge OH sites (asymmetric Brönsted interactions). This allowed facile access of Cu sites to the monomer and HSO₃ ^? cocatalyst from both sides, resulting in smoother initiation effect.     

Novel multiferroic La0.95Sb0.05FeO3 orthoferrite

A series of La_1−xSb_xFeO₃ was prepared using the conventional solid state method. XRD revealed the formation of the orthorhombic structure with space group Pbnm. The data showed that, the molar magnetic susceptibility and coercive field H_C were increased from 9.16 × 10⁻³ to 26.9 × 10⁻³ emu g⁻¹ mol and 1196 to 5465 Oe from for LaFeO₃ to La_0.95Sb_0.05FeO₃, respectively. The coercive field (H_C) of the sample with x = 0.05 increased 6 times than that of the parent LaFeO₃ and the saturation magnetization (M_s) was increased from 0.1614 emu g⁻¹ for the parent LaFeO₃ to 0.2654 emu g⁻¹ for the doped sample_. The dielectric constant (?′) was increased with increasing the Sb³⁺ content. The ac conductivity (σ) increases from 2.36 × 10⁻³ Ω⁻¹ m⁻¹ for the LaFeO₃ to 30 × 10⁻³ Ω⁻¹ m⁻¹ for the sample La_0.95Sb_0.05FeO₃ at T = 553 K and frequency 1 MHz. The sample La_0.95Sb_0.05FeO₃ is concluded to be a novel single phase multiferroic material.     

Effect of combining Al,Mg, Ce or La oxides to extracted rice husk nanosilica on the catalytic performance of NiO during COx-free hydrogen production via methane decomposition

Amorphous nanosilica powder was extracted from rice husk and used as a catalyst support as well as a starting material for the preparation of different binary oxides, i.e., SiO₂Al₂O₃, SiO₂MgO, SiO₂CeO₂ and SiO₂La₂O₃. A series of supported nickel catalysts with the metal loading of 50 wt % were prepared by wet impregnation method and evaluated in methane decomposition to “CO_x-free” hydrogen production. The fresh and spent catalysts were extensively characterized by different techniques. Among the evaluated catalysts, both Ni/SiO₂Al₂O₃ and Ni/SiO₂La₂O₃ catalysts were the most active with an over-all H₂ yield of ca. 80% at the initial period of the reaction. This distinguishable higher catalytic activity is mainly referred to the presence of free mobile surface NiO and/or that NiO fraction weakly interacted with the support easily reducible at low temperatures. The Ni/SiO₂CeO₂ catalyst has proven a great potential for application in the hydrogen production in terms of its catalytic stability. The formation of Mg_xNi_(1?x)O solid solution caused the Ni/SiO₂MgO catalyst to lose its activity and stability at a long reaction time. Various types of carbon materials were formed on the catalyst surface depending on the type of support used. TEM images of as-deposited carbon showed that multi-walled carbon nanotubes (MWCNTs) and graphene platelets were formed on Ni/SiO₂, while only MWCNTs were deposited on all binary oxide supported Ni catalysts.     

Toward 6G Communication Networks: Terahertz Frequency Challenges and Open Research Issues

Future networks communication scenarios by the 2030s will include notable applications are three-dimensional (3D) calls, haptics communications, unmanned mobility, tele-operated driving, bio-internet of things, and the Nano-internet of things. Unlike the current scenario in which megahertz bandwidth are sufficient to drive the audio and video components of user applications, the future networks of the 2030s will require bandwidths in several gigahertzes (GHz) (from tens of gigahertz to 1 terahertz [THz]) to perform optimally. Based on the current radio frequency allocation chart, it is not possible to obtain such a wide contiguous radio spectrum below 90 GHz (0.09 THz). Interestingly, these contiguous blocks of radio spectrum are readily available in the higher electromagnetic spectrum, specifically in the Terahertz (THz) frequency band. The major contribution of this study is discussing the substantial issues and key features of THz waves, which include (i) key features and significance of THz frequency; (ii) recent regulatory; (iii) the most promising applications; and (iv) possible open research issues. These research topics were deeply investigated with the aim of providing a specific, synopsis, and encompassing conclusion. Thus, this article will be as a catalyst towards exploring new frontiers for future networks of the 2030s.