Dissertação
Avaliação de catalisadores de cobre derivados de hidróxidos duplos lamelares para reação de deslocamento água-gás
Fecha
2013-03-11Registro en:
RIBEIRO, Glênio Rosinski. EVALUATION OF COPPER-BASED CATALYSTS DERIVED FROM LAMELAR DOUBLE HYDROXIDES FOR WATER-GAS SHIFT REACTION. 2013. 92 f. Dissertação (Mestrado em Engenharia) - Universidade Federal de Santa Maria, Santa Maria, 2013.
Autor
Ribeiro, Glênio Rosinski
Institución
Resumen
Hydrogen is considered the fuel of the future, due to its high energy density
and its application in fuel cells. Hydrogen is mainly obtained by light hydrocarbons
reforming. In this process, the reaction product is a gas mixture composed by
hydrogen, carbon monoxide and dioxide. However, carbon monoxide (CO)
concentration in this mixture is extremely high for some applications, such as
ammonia synthesis and fuel cells processes, where CO acts as a poison for some
types of catalysts. To remove CO excess and improve hydrogen yield in reforming
processes, it is used the Water-Gas Shift Reaction, which occurs in two steps: at high
temperatures, around 400°C with Fe-Cr catalysts; and at low temperatures, around
250°C with Cu-Zn catalysts. The goal of this work was to develop and to evaluate
copper, zinc and aluminum based catalysts derived from Lamellar Double
Hydroxides (LDH) for the low temperature Water-Gas Shift Reaction. LDH, also
called hydrotalcite-like materials, have useful properties for catalysis, such as
homogeneous metal distribution throughout its structure, improving thermal stability
and catalytic activity. An experimental design for the composition variables, Cu/Zn
and (Cu+Zn)/Al molar ratios, was used, besides the aging treatment influence over
LDH, which was verified by replicating the experiments in two groups: with and
without aging. The catalysts were prepared by the co-precipitation method; and it
was analyzed the influence of preparation conditions over their physical-chemical
properties, such as composition, specific area, porous volume and diameter, as well
as catalytic activity in low temperature Water-Gas Shift Reaction. The presence of
Cu/Zn/Al LDH phase in all prepared catalysts was verified. In some samples, there
were a few impurities, like malachite and aurichalcite in aged catalysts, and zinc and
copper oxides in not aged materials. The aging step also affected the way the Cu/Zn
and (Cu+Zn)/Al molar ratios influence the textural properties and the catalytic activity.
In aged catalysts, the specific area does not show a strong dependency on the
composition. However, these catalysts appear to have higher thermal stability in long
period reactions. Experimental design allowed a better study of the influence of
composition variables on catalysts final characteristics, aiding future studies in the
synthesis of this type of material.