2011 YÜksek lisans tez özetleri

Preparatıon And Characterızatıon Of Nıckel Based Catalysts Wıth Polyol Method

Since the powders of nickel posses good catalytic, electronic and magnetic properties they are widely used in numerous applicatons. The morphology, size and other properties of nickel nanoparticles change due to initial materials, preparation method and conditions of synthesis. Especially, the efficiency of nickel particles used as catalyst is directly related with synthesis method. As a preparation method; the traditional method such as, sol-gel, microemulsion, co-precipitation, chemical vapour deposition used and processes, that are alternative to these, were developed.

Polyol method is one of the methods prefered at the synthesis of nickel based catalysts. In this work; synthesis of nickel catalysts which showed high activity and selectivity, loaded onto alumina support with determinated amounts, at appropriate size and morphology. Comparatively to other catalyst preparation methods in the literature; it is thought that polyol method will be a good alternative for treatment of the existing problems, such as, sintering, coking, phase change, causing deactivation. This synthesis method, that provides obtaining nano sized particles, is an economic and simple process. The main advantages of this method are, it does not need high reaction temperatures and do not require calcination process which causes sintering. Since the reduction processes are carried out in solution media there is not a need for an extra processing and because of this reason formation and growth steps could be controlled. Owing to polyol method has different synthesis parameters, preparation of nano-structured particles with different properties is possible.

Nickel catalysts synthesized in this thesis tested in reaction of catalytic partial oxidation of methane that is an important hydrogen production process. Today, in hydrogen production, there have been many researches done to develop alternative processes and catalytic partial oxidation of methane (CPOM) has come forth as a good alternative. It doesn’t require an external heat because of being slightly exotermic and occurs faster 10 to 100 times than steam reforming, therefore small reactors could be used. Thus, by lowering the total investment and production costs, hydrogen production cost could be lowered. Many catalysts have been worked on partial oxidation of methane and it has been seen that noble metal catalysts (Rh, Pt, Ru, Ir) and nickel (Ni) based catalysts are active and selective for this reaction. Although, noble metal based catalysts are stable and active, because of their high cost and low availability, the best alternative have thought to be nickel based catalysts. When literature was examined, studies in this subject would be the first in own field due to the lack of study made by polyol method for synthesis of these catalysts.

In this thesis work, catalysts with 10% (by weight) Ni loaded to support were synthesized by using polyol method, were characterized and their performances were investigated for methane partial oxidation reaction. Effects of reaction parameters, systematically changing, on size, morphology and loading amounts onto support examined. While obtained catalysts showed 85 – 92 % CH₄ conversions under the flow rate of 157500 l/kg hr (CH₄:O₂:N₂=2:1:4), 1 atm pressure and at 800°C, H₂ selectivities were founded nearly 90 - 97 % in CPOM. Among the prepared catalysts % 10 Ni/Al₂O₃-5PVP and % 10 Ni/Al₂O₃-snr2PVP gave the highest conversion value of 92 %. The highest H₂ selectivity has been 97 %.