IN SITU INFRARED STUDY OF ADSORBED SPECIES DURING CATALYTIC OXIDATION AND CARBON DIOXIDE ADSORPTION
Hydrogen is considered to be the fuel of the next century. Hydrogen can be produced by either water splitting using the solar or nuclear energy or by catalytic cracking and reforming of the fossil fuels. The water splitting process using solar energy and photovoltaics is a clean way to produce hydrogen, but it suffers from very low efficiency. A promising scheme to produce H2 from natural gas involves following steps: (i) partial oxidation and reforming of natural gas to syngas, (ii) water-gas shift reaction to convert CO in the syngas to additional H2, (iii) separation of the H2 from CO2, and (iv) CO2 sequestration. The requirements for the above scheme are (i) a highly active coke resistant catalyst for generation of syngas by direct partial oxidation, (ii) a highly active sulfur tolerant catalyst for the water-gas shift reaction, and (iii) a low cost sorbent with high CO2 adsorption capacity for CO2 sequestration. This dissertation will address the mechanisms of partial oxidation, CO2 adsorption, and water-gas shift catalysis using in-situ IR spectroscopy coupled with mass spectrometry (MS). The results from these studies will lead to a better understanding of the reaction mechanism and design of both the catalyst and sorbent for production of hydrogen with zero emissions. Partial oxidation of methane is studied over Rh/Al2O3 catalyst to elucidate the reaction mechanism for synthesis gas formation. The product lead-lag relationship observed with in situ IR and MS results revealed that syngas is produced via a two-step iv reforming mechanism: the first step involving total oxidation of CH4 to CO2 and H2O and the second step involving the reforming of unconverted methane with CO2 and H2O to form syngas. Furthermore, the Rh on the catalyst surface remains predominantly in the partially oxidized state (Rhä+ and Rh0). For the water-gas shift reaction, addition of Re to the Ni/CeO2 catalyst enhanced the water gas shift activity by a factor of three. The activity of the Ni-Re/CeO2 catalyst was reduced by only 20% in the presence of sulfur compared to a 50% reduction with the Ni/CeO2 catalyst. These results show that Re not only promotes the water-gas shift reaction but also enhances the sulfur tolerance of the Ni/CeO2 catalyst. Novel amine based solid sorbents have been developed to capture CO2 reversibly using temperature-swing adsorption process. The IR study shows that CO2 adsorbs on amine grafted SBA-15 to form carbonates and bicarbonates. Comparison of monoamine and diamine-grafted SBA-15 showed that diamine grafted SBA-15 provides almost twice the active sites for CO2 adsorption. The adsorption of SO2 on the amine-grafted SBA-15 revealed that SO2 adsorbs irreversibly and the sorbent cannot be regenerated under normal operating conditions. Results of these studies can be used to enhance the overall conversion of CH4 to H2 thus lowering the cost of H2 product.
School:The University of Akron
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:co2 adsorption methane partial oxidation water gas shift insitu infrared spectroscopy mass spectrometry
Date of Publication:01/01/2005