A new approach for synthesis of well-crystallized Y zeolite from bentonite and rice husk ash used in Ni-Mo/Al2O3-Y hybrid nanocatalyst for hydrocracking of heavy oil

A series of Ni-Mo/Al₂O₃-Y hybrid nanocatalysts were synthesized for hydrocracking of heavy oil. The well crystallized Y zeolite was synthesized from mineral bentonite and rice husk ash by a two-step synthesis method. The solution combustion method was applied to develop a fast and simple technique for preparing of alumina-supported NiMo catalyst with high hydrodesulfurization activity. Such activity may be due to the morphological and textural modification as a consequence of the release of a high amount of exhaust gases during the combustion process. The XRD analysis revealed that the P zeolite was a competitive phase presented in the obtained product that could be eliminated using a two-step synthesis method. Compared to a one-step method, the pore volume and external surface area of the synthesized zeolite by the two-step method increased by 74 and 62%, respectively. The hydrocracking results illustrated that the synthesized zeolite was able to convert 66% of heavy oil to lighter products and reduce the viscosity up to 60%. Furthermore, the amount of sulfur removal was found to be 58%. The spent catalyst characterization suggested that the type of deposited coke was hard coke with the unsaturated aromatic ring which could be responsible for the pores blockage after the cracking reaction.     

Hydrocracking and hydrodesulfurization of diesel over zeolite beta-containing NiMo supported on activated red mud

NiMo nanocatalysts supported on activated red mud with different zeolite beta contents were successfully prepared by impregnation technique. Their hydrocracking and hydrodesulfurization activities were evaluated with two different kinds of diesel feed (iso diesel and heavy diesel) in a fixed bed reactor at ambient pressure and 500 °C. Physico-chemical properties of synthesized samples were characterized using the methods of XRF, XRD, FESEM, BET, FTIR and NH₃-TPD. The results indicated that zeolite incorporation resulted in a significant increase in specific surface area (BET result) and acidic strength (TPD result) of nanocatalysts. FESEM analysis confirmed that the particles size of zeolite-containing NiMo/ARM was less than 100 nm and the average size of particles was about 30 nm. Hydrocracking results illustrated that incorporation of zeolite beta improved cracking activity considerably. In addition, NiMo nanocatalyst containing 37.5 wt% of zeolite had the highest yields of desirable products (naphtha, kerosene and diesel) and the highest conversion. Moreover, the flash point and viscosity of the liquid product decreased notably the nanocatalysts with 37.5 wt% and 12.5 wt% of zeolite were able to remove approximately 96% and 72% of the sulfur content of iso diesel and heavy diesel, respectively.     

Rice husk ash-based silica-supported iron catalyst coupled with Fenton-like process for the abatement of rice mill wastewater

An economically efficient and eco-benign new approach was performed for the treatment of rice mill wastewater by Fenton-like process using rice husk ash (RHA)-based silica-supported iron catalyst. The detailed characterization of the prepared catalyst was described by SEM, XRD, and FT-IR. The maximum COD reduction of 75.5 % was achieved at response surface-optimized conditions that constitutes of catalyst dose 4.12 g/L, H₂O₂ concentration 4.2 g/L and pH 3.2. The non-toxic nature of the treated rice mill effluent using green catalyst was revealed by phytotoxicity. Meticulous efforts have been made for judicious utilization of one waste (RHA) against another serious waste (rice mill wastewater) abatement of the same industry. Findings clearly established that the proposed designed scheme offered a complete sustainable solution towards minimization of various wastes generated from rapidly growing rice mills.     

Synthesis of zeolite T powders by direct dissolution of rice husk ash: an agro-waste material

Rice husk ash (RHA), an agro-waste material, was used for the synthesis of zeolite T powders following a simple and cost-effective process. In this process, silica as silicate was directly extracted from solid RHA particles in the presence of aluminate and other aqueous-based precursor materials. The synthesized powders were characterized by thermogravimetry analysis, differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, N₂ physisorption measurements, and field emission scanning electron microscopy (FESEM). Crystallization of zeolite T powders was noticed at 100 °C/24 h. The vibration bands of the powders at around 580 and 630 cm^?1 indicated the characteristic double six ring of zeolite T. Micropore surface area and micropore volume of zeolite T increased significantly at 100 °C/72 h. FESEM images showed ellipse-shaped morphology of the powders, and their aspect ratio increased with increase in reaction time. A tentative mechanism was proposed for direct extraction of silica as silicate from RHA, and its conversion to zeolite T in the presence of other aqueous-based precursors by a single step process.     

Influence of 15 and 80 nano-SiO2 particles addition on mechanical and physical properties of ternary blended concrete incorporating rice husk ash

This study demonstrates the effects of SiO₂ nanoparticles as additives with two different sizes of 15 and 80?nm on compressive strength and porosity of rice husk ash (RHA) blended concrete. Up to 20% of ordinary Portland cement (OPC) was replaced by RHA with average particle size of 5 micron. Also, SiO₂ nanoparticles were added to the above mixture at four different weight percentages of 0.5, 1.0, 1.5 and 2.0 and cured in lime solution. The results indicated that compressive strength of Portland cement–nano SiO₂–rice husk ash (PC–NS–RHA) ternary blended concrete was considerably increased. Moreover, the total amount of porosity decreased to a minimum with respect to the control concrete. This improvement was observed at all the curing ages and replacement levels, but there was a gain in the optimal point with 20% of RHA plus 2% of 80?nm SiO₂ particles at 90 days of curing.     

金属氧化物负载RuS2的加氢脱硫异相催化

CoMo／A1203和NiMo／A1203等催化剂体系已经基本实现了工业化,尽管RuS2比它们的加氢脱硫活性会更好,因其成本较高而致使到目前为止尚不能完全实现工业化的应用,但是该催化剂体系仍是今后发展的重要趋势之一。本文从理论分析和实验方法总结了金属氧化物负载RuS2催化剂的制备、性质及其在加氢脱硫方面的活性与应用,并且描述了今后寻找新载体以及纳米RuS2发展方向。     

Effect of preparation technique on the properties of Mo-containing Al-MCM-41

The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo) is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after activation with mixture H₂ + H₂S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied. A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated sample than on the mechanochemically treated one.     

Preparation of lamellar-stacked TS-1 and its catalytic performance for the ammoximation of butanone with H<Subscript>2</Subscript>O<Subscript>2</Subscript>

A SiO₂ particle was prepared with different alkali sources, and then lamellar-stacked TS-1 catalysts were hydrothermally synthesized using the SiO₂ particle as a silica source. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra, nitrogen adsorption–desorption and UV–vis absorption spectra were used to characterize the TS-1 catalysts. The effect of the alkali source during the preparation of the SiO₂ particle on the textural properties and catalytic performance of the TS-1 catalyst was thoroughly investigated. The TS-1 catalyst that was prepared with a SiO₂ particle using tetrapropylammonium hydroxide (TPAOH) as an alkali source (TS-1-TPAOH) possessed more meso- and macro-pores and a higher framework Ti content than the catalyst that was prepared with a SiO₂ particle using NH₃·H₂O as an alkali source (TS-1-NH₃·H₂O). As a result, the TS-1-TPAOH catalyst had a better catalytic performance for butanone ammoximation with H₂O₂ than conventional TS-1 and TS-1-NH₃·H₂O catalysts. Furthermore, the influences of reaction conditions, including reaction temperature, reaction time, the amount of catalyst and the molar ratio between H₂O₂ and butyl ketone oxime on the catalytic performance of the TS-1-TPAOH catalyst were evaluated. The unique structure of the lamellar-stacked TS-1 catalyst can effectively avoid the diffusing of large reactant molecules into zeolite channels and has potential applications in other oxidation reactions.     

MoO3-based HDS catalyst obtained by the polymeric precursor method

The NiCoMo/γ-Al₂O₃ catalyst was synthesized by polymeric precursor method and it was structurally and morphologically characterized by X-ray diffraction, infrared spectroscopy, nitrogen adsorption measurements. Besides the structural and morphological characterization, a catalytic performance test for the hydrodesulfurization process (HDS) using thiophene was also carried out, in a continuous flow reactor. The method proposed for the synthesis of such a catalyst led to an excellent performance of the HDS process, converting more than 97% of thiophene into iso-butane, 1-butene, n-butane, trans-2-butene and cis-2-butene.     

Removal of Cr(VI) and As(V) from aqueous solutions by HDTMA-modified zeolite Y

The synthesized zeolite NaY from rice husk ash (RHA) and the commercial zeolite NaY both modified with surfactants in amounts equal to 50%, 100% and 200% of their external cation exchange capacity (ECEC) were used to remove chromate and arsenate anions from aqueous solutions. While the unmodified zeolite Y had little or no affinity for the Cr(VI) and As(V) anionic species, the surfactant-modified zeolite Y (SMZY) showed significant ability to remove of these anions from the aqueous solutions. The highest chromates and arsenates adsorption efficiency was observed from solutions of pH values 3 and 8, respectively because of the dominance of the univalent species of both anions. The adsorption equilibrium data were best fitted with the Langmuir isotherm model with the highest removal capacities observed for the SMZY initially prepared considering the hexadecyltrimethyl ammonium (HDTMA) amount equal to the 100% of the ECEC of zeolite Y. Synthesized SMZY remove Cr(VI) and As(V) more than the corresponding commercial one due to its lower silica to alumina ratio. Thus, the HDTMA-covered modified zeolite Y synthesized using RHA can be used to remove Cr(VI) and As(V) from water.     

X-ray diffraction analysis of silicon prepared from rice husk ash

Polycrystalline silicon has been prepared by metallothermal reduction of rice husk ash, which contains a considerable amount of amorphous silica. Acid-leached rice husk was burnt at a temperature of 620° C to obtain rice husk ash (RHA). RHA was then reduced with magnesium and major impurities were minimized or removed by an acid leaching process. The end-product was analysed using X-ray diffraction and mass spectrometric techniques. It was found that the powdered silicon obtained from magnesium reduction of RHA had a very low impurity concentration indicating that rice husk, which is an agricultural waste, is a potential source of metallurgical and solar-grade silicon.     

Optimized synthesis method for K/Co3O4 catalyst towards direct decomposition of N2O

The potassium-doped Co₃O₄ catalysts were prepared by impregnation of potassium sources on commercial cobalt carbonate and on the precursors synthesized by homogeneous precipitation, combustion with glycine, gradual oxidation, and hydrothermal methods. The activities of these catalysts for the direct decomposition of nitrous oxide in the presence of oxygen with or without water vapor were examined. The effects of potassium sources on the catalyst activity were also examined by impregnation of various potassium salts on commercial cobalt carbonate. The catalyst prepared by impregnation of an aqueous solution of KOH on commercial cobalt carbonate showed the highest activity. The catalysts prepared by various methods were analyzed by powder X-ray diffraction, N₂ adsorption, scanning electron microscope, temperature-programmed reduction with H₂, temperature-programmed desorption of O₂, and X-ray photoelectron spectroscopy. These results suggest that crystallite size and reduction property are key factors for the activity of the catalyst for the direct decomposition of nitrous oxide in the presence of oxygen.     

Optimizing conditions for preparation of MnOx/RHA catalyst particle for the catalytic oxidation of NO

Rice husk ash (RHA) was utilized as support to synthesize MnOx/RHA catalyst by incipient wetness impregnation. In order to detailedly investigate the influence of preparation variables on the catalytic activity of MnOx/RHA for NO oxidation, the quadratic regression orthogonal rotation design (QRROD) was employed. An empirical model was developed to correlate preparation variables with the conversion of NO to NO₂. The surface species and morphology of the catalyst were also analyzed by SEM and XRD, respectively. It was found that most of MnOx supported on RHA were granular with micron-size and in the form of amorphous phase. The preparation variables except for calcination time (x₂) had significant effect on the catalytic activity of MnOx/RHA. The model could accurately describe the relationship between the preparation variables and NO conversion through the analysis of variance (ANOVA) and the comparison of experimental results and predicted results. The particles size of MnOx was increased from 0.1 to 1.0 μm, as the calcination temperature was raised from 200 to 800 °C, and the fraction of crystal MnOx also increased. The surface structure of RHA was markedly affected by incineration temperature. With incineration temperature increasing, the surface structure becomes compacter.     

Use of rice husk ash in sandcrete blocks for masonry units

Different mix proportions of sand, cement and rice husk ash (RHA) were studied for use in sandcrete blocks. Optimum water/(cement+RHA) ratios were determined at different mix proportions. Compressive strengths of various mix proportions at 7, 28 and 60 days were also determined. The optimum water/(cement+RHA) ratio increased with rice husk ash contents. Test results showed that up to 40% RHA could be added as a partial replacement for cement without any significant change in compressive strength at 60 days. Compressive strengths of various mix proportions were compared with British Statutory minimum compressive strengths of bricks for various walls and it was found that sandcrete blocks of 1∶5 mortar mixes with 40% RHA (by weight of cement) could be used in both load and non-load bearing walls.     

Water absorption control of ternary blended concrete with nano-SiO2 in presence of rice husk ash

In the current study, the effects of SiO₂ nanoparticles as additive with two different sizes of 15 and 80?nm on water absorption of rice husk ash (RHA) blended concrete have been investigated. Concrete samples were prepared by replacing 10, 15 and 20?wt% of cement with RHA and 0.5, 1.0, 1.5 and 2.0% of cement with SiO₂ nanoparticles followed by curing in lime solution for 7, 28 and 90?days. The results indicated that the resistance to water absorption of Portland cement?Cnano SiO₂?Crice husk ash (PC?CNS?CRHA) ternary blended concrete was considerably improved with respect to the control concrete. This improvement was observed at all curing ages and replacement levels but the optimal point was reached for 20% of RHA incorporating 2% of 80?nm SiO₂ particles at 90?days of curing. Fast formation of C?CS?CH gel in the presence of ultra high active nano-sized SiO₂ and micron level RHA particles together with their high filler effect may result in a continuous cement paste with the lowest weak zones. It has been concluded that the use of novel ternary blended concrete (PC?CNS?CRHA) provides significant reduction in the water absorption of concrete.     

Hydrothermal synthesis and characterization of silica nanowires using rice husk ash: an agricultural waste

One-dimensional structures are the smallest dimension structures that represent a unique system for analyzing phenomena at the Nanoscale. Nanowires, which can be used for space confined transport phenomena and enhanced optical properties, are believed to play significant role in the function and integration of Nano electronics and Nano optoelectronics devices. Nanowires with well controlled morphology and extremely high aspect ratio can be obtained by various complex techniques but the demand of upcoming future technology is to synthesize large scale 1D nanostructures with simple and efficient cost effective methods. With this view, in the present study, large scale amorphous silica nanowires (SiO₂ NWs) were synthesized from rice husk ash using Fe₂O₃ assisted hydrothermal method and characterizations of these nanowires along with rice husk ash (RHA) containing porous silica, were done using various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy and photoluminescence (PL). The structural study of silica nanowires were studied using XRD, indicating the amorphous phases of silica in both RHA as well as nanowires. The chemical composition along with symmetric or anti-symmetric starching bonds of amorphous SiO₂ NWs and RHA was confirmed using FTIR. The morphological study was done using SEM and TEM. The SiO₂ NWs so obtained have diameter in the range from 15 to 35 nm and length about 0.5 µm. In optical study, the enhanced band gap of amorphous SiO₂ NWs as compared to RHA was observed using UV–Vis spectroscopy. PL spectroscopy shows strong blue light emission by silica nanowires as compare to RHA. This study opens up new areas for research to modulate optoelectronic properties of SiO₂ nanowires for the novel device application.     

Synthesis of zeolites NaA and analcime using rice husk ash as silica source without using organic template

Silica was extracted from Fajr rice husk ash (RHA) with approximately 97% purity, converted to sodium and potassium silicate solutions and used as silica source for the synthesis of NaA and analcime zeolites. NaOH and KOH without organic templates were used in the synthesis of NaA and analcime zeolite, respectively. Conventional heating and microwave-assisted hydrothermal were used in zeolite synthesis. Zeolites were characterized with XRD, SEM and IR spectroscopy. Heating time and Si/Al ratio were optimized for the synthesis of zeolites.     

Synthesis and catalytic ammoxidation performance of hierarchical TS-1 prepared by steam-assisted dry gel conversion method: the effect of TPAOH amount

The hierarchical titanium silicalite-1 (TS-1) was synthesized by the steam-assisted dry gel conversion method in one step and characterized by XRD, SEM, N₂ adsorption/desorption, UV–Vis, FT-IR, and Raman spectroscopies. And its catalytic activity was tested for ammoxidation of methyl ethyl ketone with hydrogen peroxide as oxidant. The results show that the amount of tetrapropylammonium hydroxide (TPAOH) as template has a major influence on the physicochemical and catalytic properties of the hierarchical TS-1 prepared. When lower amount of TPAOH (TPAOH/SiO₂ = 0.08 mol) was used, hierarchical TS-1 can be successfully synthesized. With an increase in TPAOH amount in synthesis solution, the crystal size of TS-1 is decreased and mesoporous surface area is increased; if the excess template was used in the synthesis of TS-1, more extra-framework Ti would be formed in the TS-1 samples prepared. The hierarchical TS-1 exhibits higher catalytic activity than TS-1 prepared hydrothermally for ammoxidation of methyl ethyl ketone. Using hierarchical TS-1 synthesized under TPAOH/SiO₂ = 0.18 as the catalyst, which has more tetrahedrally coordinated Ti species in the TS-1 framework, 94.2 % conversion of reactant and 100 % selectivity to methyl ethyl ketone oxime can be obtained after 2 h of reaction at 70 °C.     

Interaction of V2O5-NaY zeolite with H2S and SO2

V₂O₅-NaY zeolite catalyst was prepared by vacuum impregnation of ammonium metavanadate solution in water on NaY-zeolite (zeolite). The slurry was filtered, washed, dried, and calcined at 600°C. On heating the catalyst at 450°C in vacuum, VO²⁺ species were detected by e.s.r. It was observed that the electron-accepting and -donating sites increased when V₂O₅ or vanadium species were loaded on it. Vanadium species poisoned the active sites of the zeolite that were responsible for the formation of SO₂⁻ ions. Pretreated V₂O₅-NaY zeolite with SO₂ plays an important role in the formation of VO²⁺ species when it is treated with H₂S at room temperature. V₂O₅-NaY zeolite can be used for the reduction of SO₂ by H₂S.     

含US-SSY分子筛的Ni-W-γ-Al2O3体系的EXAFS研究

运用EXAFS技术分别对含有自冷和急冷US-SSY分子筛的Ni－W－γ－Al_2O_3样品中的w的LⅢ吸收边和Ni的K吸收边进行了结构分析。结果表明分子筛超稳化后的冷却速率对样品中原子的局域结构有影响，进而影响了样品的催化活性。急冷样品中W的分散度比自冷样品差，其八面体结构含量较高，并有钨钼氧原子簇产生。但急冷催化样品中Ni具有较高的分散度，Ni-W间距小，较易形成“Ni－O－W”物种。由于八面体结构中的氧在加氢脱硫反应中较易被硫取代，且“Ni-O-W”物种是HDS反应的活性前驱体，导致急冷样品具有较高的HDS活性。加快分子筛超稳化后的冷却速率可提高催化剂样品的活性。