M.D. Romero

Bifunctional catalyst NiHZSM-5: effects of the nickel incorporation method

Abstract The influence of the method used for the metal incorporation, technique and precursor compound on the hydroisomerization of n-decane over the bifunctional Ni HZSM -5 catalyst was studied. Two preparation methods, ion exchange and impregnation, using different nickel precursors were tested. Temperature-programmed desorption of ammonia (TPDA), thermogravimetric analyses (TGA), temperature-programmed reduction (TPR), electronic microscopy (SEM, TEM) and atomic absorption spectroscopy (AA) techniques were used to characterize the catalysts. The n-decane hydroisomerization was selected as a test reaction to determine the catalyst activity. These experiments were carried out in a basket type reactor, using a catalyst ground with sodium montmorillonite. The method of nickel incorporation was found to be an important indicator for the activity and selectivity of the catalyst, having a significant influence not only on its hydrogenating properties but also on its acidity. The nickel incorporation technique was mainly affecting the nickel dispersion, while it was affecting both functions, metallic and acid, when the precursor was modified.

Acidity modification during the agglomeration of ZSM-5 with montmorillonite

Abstract Ammonia TPD analyses of ZSM-5 zeolites of three Si/Al ratios (15, 30, 43) agglomerated with sodium montmorillonite revealed a noticeable modification on the acid properties of the bound zeolites as compared with the raw materials. An initial increase of the proportion of the weak acidity was found on the agglomerated zeolites, though the total and strong acidity decreases. The higher the Si/Al ratio of the zeolite, the higher is this increase. After several steps of ion exchange of the bound zeolites, the acidity reaches the expected values again, and the total and strong acidities are enhanced at the expense of the weak acidity. These results were related to a solid-state ion exchange between protons of the zeolite and cations of the clay during the calcination subsequent to the agglomeration.

Epitaxial Solar Cells Over Upgraded Metallurgical Silicon Substrates: The Epimetsi Project

In order to overcome the shortage of silicon feedstock that is currently affecting the photovoltaic industry, many efforts are being dedicated to the search of alternative substrates for solar cells. One of the possible solutions is to use low-cost substrates of upgraded metallurgical silicon, for which there are no supply issues. The solar cell is built on a thin layer of high quality silicon which is epitaxially grown over this substrate, with the use of a high throughput epitaxial reactor of novel design. This reactor can be fed with electronic grade source gases or with gases obtained in situ from metallurgical silicon. A reactor prototype has been constructed with a capacity of 50 wafers per run and a deposition velocity of approximately 2 microns per minute. The production of chlorosilanes by Si etching and the recirculation of gases for maximum efficiency are being studied. A solar cell process specific for these substrates has been developed, achieving an efficiency of 12,8%. Further improvements on the solar cell process are under investigation, with special emphasis on light trapping by plasma texturing and the application of a porous Si layer as internal reflector. A preliminary market study has been performed to understand the role of silicon feedstock in the current photovoltaic market and its projection in the next decades, looking at the expected role of epitaxial solar cells