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One of the most important challenges for 21st century is the use of nanoscience in the development of sustainable and renewable energy production schemes. In the first decade of the current century, the emergence of a new field in catalysts science, named nanocatalysis, has attracted the attention to researchers. Generally, good potential catalysts have a large surface to volume ratio of nanoparticles compared to bulk materials. It is widely known in the biomass conversion field that changes in acidic properties, the type of metal content and porosity of catalysts have an effect on the performance of the catalyst. However, to improve the product quality, new types of catalysts must be developed. Blending  biomass with coal and optimization of the experimental conditions also improves the quality of products. There are several methods to prepare nanosized materials. These materials may be used directly or in the form of supported nanoparticles on solids such as mesoporous oxides (Al2O3, SiO2, ZrO2, TiO2 etc.), carbon, carbon like materials such as graphene or interconnected carbon nanosheets, zeolites etc. Some typical methods for nanocatalyst preparation are impregnation, precipitation, chemical vapor deposition and electrochemical deposition:

  • Precipitation and impregnation methods are simple, cheap and well-studied but it is difficult to control the size of the particles.
  • Chemical vapor deposition is widely used in the electronics industries but it is an expensive method.
  • Electrochemical deposition is an inexpensive method which doesn’t require high temperatures and concentration. This method allows good control of size and chemical properties of the deposited nanomaterials but usually forms one dimensional nanomaterials.

In most research, impregnation and precipitation methods have been used for biomass catalysts preparation. However, these two methods don’t encapsulate the metal particles inside the support. They only stay on the surface of the support, which is easily washed out, rather than participating in the reaction during biomass gasification because of very weak metal support interactions. Therefore, from this point of view, these catalyst preparation technologies remain an art, and rational design of catalysts still remains a challenge to the catalysis community.


Figure 1: TEM images of 11% Ni-Al2O3 catalysts (size of nickel particles (i) 2nm (ii) 9nm (iii) 23nm)

Nowadays, the colloidal synthesis method offers new opportunities for size-controlled nanocatalysts. Four components such as metal precursor, surfactant, solvent and reducing agent are needed for the colloidal synthesis of metal nanoparticles. For a typical synthesis, desired precursors are selected and dissolved into the solvent in the presence of surfactants. The reduction process then proceeds at an elevated temperature to generate metallic nanoparticles by introducing a reducing agent. Figure 1 shows the size controlled nickel nanoparticles on alumina support.

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