Rooh Ullah

Effect of vanadium contamination on the framework and micropore structure of ultra stable Y-zeolite.

Y-zeolites are the main component of fluid catalytic cracking (FCC) catalyst for conversion of crude petroleum to products of high demand including transportation fuel. We investigated effects of vanadium which is present as one of the impurities in FCC feedstock on the framework and micropore structure of ultra-stable (US) Y-zeolite. The zeolite samples were prepared and characterized using standard techniques including: (1) X-ray diffraction, (2) N2 adsorption employing non local density functional theory method, NLDFT, (3) Transmittance and Pyridine FTIR, (4) Transmittance electron microscopy (TEM), and (5) (27)Al and (29)Si MAS-NMR. Results revealed that in the presence of steam, vanadium caused excessive evolution of non inter-crystalline mesopores and structural damage. The evolved mesopore size averaged about 25.0nm at 0.5wt.% vanadium loading, far larger than mesopore size in zeolitic materials with improved hydrothermal stability and performance for FCC catalyst. A mechanism of mesopore formation based on accelerated dealumination has been proposed and discussed. Vanadium immobilization experiments conducted to mitigate vanadium migration into the framework clearly showed vanadium is mobile at reaction conditions. From the results, interaction of vanadium with the passivator limits and decreases mobility and activity of vanadium into inner cavities of the zeolite capable of causing huge structure breakdown and acid sites destruction. This study therefore deepens insight into the causes of alteration in activity and selectivity of vanadium contaminated catalyst and hints on a possible mechanism of passivation in vanadium passivated FCC catalyst.

Remarkably high performance of clew-like ZnO superstructure in reactive adsorption desulfurization

In this study, a clew-like ZnO superstructure was synthesized by a copolymer-controlled self-assembly homogeneous precipitation method. Ni was impregnated to the clew-like ZnO superstructure to obtain Ni/ZnO adsorbents. The synthesized materials were characterized by scanning electron microscopy, transmission electron microscopy, N2 sorption, X-ray diffraction, Fourier transform infrared spectrometry, and H2-temperature programmed reduction techniques. The reactive adsorption desulfurization (RADS) performance of the adsorbents was evaluated in a fixed bed reactor using thiophene in n-octane as a model fuel. Sample Ni/ZnO-4h exhibits a remarkably high performance with a sulfur capacity of 189.1 mg S g–1, which is above 6 times that of the one prepared with commercial ZnO. Characterization results show that the morphology changes from micro-clews to large solid sticks with the increase of the crystallization time. The loose and open architecture of the clew-like ZnO superstructure facilitates the diffusion of reactants/products, and prevents the adsorbent particles from breakage by supplying space for the volume expansion during the RADS process. The small nanoparticles in ZnO nanostrips result in a high sulfur adsorption capacity and also favor the dispersion of Ni, leading to an excellent RADS performance.摘要本文利用共聚物控制均匀沉淀法自组装合成了一种毛线球状ZnO超结构. 通过将Ni浸渍于该氧化锌材料上制备了一系列Ni/ZnO吸 附剂. 其中, 样品Ni/ZnO-4h在反应吸附脱硫中表现出极高的硫容量(189.1 mg S g–1), 是相同条件下使用普通商业ZnO制备的Ni/ZnO-C样 品的6倍. 毛线球状ZnO疏松开放的结构能够促进反应物/产物的扩散, 并抑制体积膨胀对吸附剂结构的破坏. 较小的ZnO颗粒在提供较高 的硫容量的同时还能促进活性组分Ni的分散, 从而导致吸附剂具有较高的反应吸附脱硫性能.