Hydrogen is one of the most important fuels for the future. It can be used directly for combustion or as a feedstock for fuel cells to generate electric energy. The advantage of hydrogen compared to fossil fuels is, that combustion only leads to water as reaction product. So, the emission of CO2, a green house gas, can be decreased. Today, hydrogen is mainly generated from fossil resources, such as crude oil or natural gas. As there use is limited, the interest for the application of renewable resources has increased rapidly during the last years. An example is glycerol, which is a by-product of the biodiesel production. In addition to the conventionally used reforming processes, aqueous-phase reforming (APR) is an energy efficient alternative, because moderate temperatures (220-250°C) and pressures (20-25 bar) are applied.
This study investigates the catalytic conversion of glycerol to hydrogen by aqueous-phase reforming on different platinum catalysts. Specially, the effect of catalyst modification, considering catalyst support, metal loading, metal dispersion and composition, as well as the effect of reaction conditions on the hydrogen yield are investigated. For catalyst preparation a variety of platinum salts was applied. Using the incipient wetness technique highly dispersed platinum catalysts with metal loadings between 1 and 10 wt.% could be prepared reproducibly. Among the support materials used, aluminum oxide was identified as the most suitable support for the APR-reaction of glycerol. Also, the structure of the aluminum oxide plays an important role, because it affects the properties of the pore system. The highest catalytic activity and selectivity to hydrogen was achieved with Puralox, a mixture of γ-, δ- and Θ-aluminum oxides, compared to catalysts prepared on Boehmite or γ-alumina. The calcination of platinum catalysts at different temperatures resulted in different platinum dispersion. In the APR-reaction of glycerol those catalyst showed similar activity, achieving a conversion of 20 % but hydrogen selectivity increased from 78 % for small particles (1.7 nm) up to 98 % for larger particles (3.2 nm). Thus, the APR-process can be called structure sensitive under those conditions. | English |