Abstract
A novel self-sustained electrochemical promotion (SSEP) catalyst for partial oxidation reforming (POXR) of hydrocarbons into synthesis gas (H2 and CO) is proposed, synthesized, experimentally evaluated and numerically analyzed. The SSEP catalyst consists of microscopic selective anodic (Ni-Cu-CeO2) and cathodic (La0.9Sr0.1MnO3) phases that are coupled via microscopic oxygen ion conduction (yttria-stabilized zirconia, YSZ) and electronic conduction (Ni-Cu) phases. A series of partial oxidation reforming (POXR) tests on a heavy hydrocarbon (n-pentadecane) and a light hydrocarbon (methane) in the temperature range between 450 and 650 °C were conducted in order to verify the effect of SSEP. The SSEP catalyst was compared with non-SSEP catalysts in short of one or more components. The performance of the SSEP catalyst was better than that of the non-SSEP catalysts in the entire temperature range. At 450 and 500°C, the n-pentadecane conversion and yield of the SSEP catalysts were respectively 2-4 folds and hundreds of folds better than those of the non-SSEP catalysts and a commercial Pt-CeO2 catalyst under the same operation conditions. These results demonstrate that the concept of SSEP catalysts can be employed to improve catalytic POXR of hydrocarbons. A kinetic model for numerical simulation of partial oxidation reforming (POXR) of hydrocarbons over the SSEP is established, and then experimentally verified. The kinetic model of SSEP-POXR consists of two parts: a conventional Langmuir-Hinshelwood (L-H) model describing normal POXR, and a new model describing the SSEP effect. The kinetic parameters of the L-H model are estimated by curve-fitting experimental results of POXR of hydrocarbons on a conventional Ni-Cu-CeO2 catalyst, whereas those for the SSEP process are evaluated using typical geometric configurations of components of the SSEP catalyst and their electrochemical properties. The following conclusions can be drawn from these studies: The experimental results of POXR of hydrocarbons show that the SSEP catalyst accelerates the POXR reaction rate remarkably at low temperature ranging from 450 to 650 °C comparing to currently widely used Ni based catalyst or even precious metal based catalyst. This concept of SSEP catalyst may provide a new route for developing high performance catalysts for hydrocarbons reforming. The kinetic model of catalytic POXR of hydrocarbons over the SSEP catalyst is established and successfully describes the SSEP-POXR process. The kinetic modeling results agree well with the experimental data in terms of the temperature impact on the fuel conversion. More importantly, the SSEP-POXR model is established based on the actual geometric configurations of the microscopic structure of the catalyst and the electrochemical properties of the materials of components of the catalyst. Thus, it can be used as a tool to predict experimental results, guide the design and optimization of the future SSEP catalyst.