Acidity as Descriptor for Methanol Desorption in B-, Ga- and Ti-MFI Zeotypes

The isomorphous substitution of Si with metals other than Al in zeotype frameworks allows for tuning the acidity of the zeotype and, therefore, to tailor the catalyst’s properties as a function of the desired catalytic reaction. In this study, B, Ga, and Ti are incorporated in the MFI framework of silicalite samples and the following series of increasing acidity is observed: Ti-silicalite < B-silicalite < Ga-silicalite. It is also observed that the lower the acidity of the sample, the easier the methanol desorption from the zeotype surface. In the target reaction, namely the direct conversion of methane to methanol, methanol extraction is affected by the zeotype acidity. Therefore, the results shown in this study contribute to a more enriched knowledge of this reaction.

Combined first-principles calculations and experimental study on the photocatalytic mechanism of natural dolomite

Natural dolomite exhibits notable photocatalytic activity due to the isomorphous substitution of Fe2+ for Mg2+ in the lattice, implying that it can be used as a low-cost photocatalyst.

Synthesis and catalytic properties of a novel copper- and manganese-substituted cerium dioxide for benzene remediation

Catalysts based on inexpensive and abundant transition metals are necessary for effective environmental remediation. In this study, a series of CuMn-CeO2 catalysts is synthesized by a simple coprecipitation method. The properties of the as-prepared catalysts are characterized by X-ray diffraction, Brunauer–Emmett–Teller analysis, scanning electron microscopy–energy-dispersive spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The introduction of dopants results in rougher surfaces with greater surface areas and pore volumes as well as more surface defects. Furthermore, the dopant-added catalysts exhibit higher activities for benzene oxidation, as the temperature required for 90% benzene removal with Cu4Mn1-CeO2 (656 K) was 231 K lower than that required with CeO2. The superior performance of the dopant-added CeO2 catalyst is attributed to the generation of defect-rich surfaces due to the isomorphous substitution of Cu and Mn in the crystal lattice of CeO2.

Structural/Texture Evolution During Facile Substitution of Ni into ZSM-5 Nanostructure vs. its Impregnation Dispersion Used in Selective Transformation of Methanol to Ethylene and Propylene

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.

Ion Exchange: The Most Important Chemical Reaction on Earth after Photosynthesis

Ion exchange is the interchange of equivalent amount of ions from the solution with ions which are swarming in a boundary of charged surface in equilibrium. It is developed due to the presence of charge in the soil colloids or layer lattice clay minerals. The source of charge developed in the colloidal surface site of soil is mainly from two processes viz. isomorphous substitution and pH dependent charge. The charge can be positive or negative due to the exchange reaction in the layer lattice. The ion exchange capacity is the sum of cation exchange capacity (CEC) and anion exchange capacity (AEC). It depends on the types of soil and the amount of charge present in the layer lattice colloidal structure. With high negative charge in the lattice surface the CEC increases and with positive charge the AEC. Ions with higher charge have larger affinity to adsorbed more strongly than lower. Ion exchange capacity in soil has the ability to retained more nutrients in the form of cations or anions making available to plant for a long time which improved the fertility of soil. Leaching loss of different nutrients from the soil is reduced by holding different ions. Ion exchange processes have been widely used for heavy metal removal for waste water treatment and water purification because of its high remedial capacity, high removal efficiency and fast kinetic. Due to its applications in agriculture, environmental management, industries, waste water treatment in mining industries, laboratory, nanotechnology, geotechnical and other soil reclamation processes it is considered as the second most important reaction in the globe after photosynthesis.