A study on co-free hydrogen production from hydrocarbons and COx elimination through pre-combustion

Abstract

The goal of this research study is to design and develop active, stable and selective alkali promoted Pt-based catalysts and activated carbon-based adsorbents for COx elimination to be used in CO-free hydrogen production and CO2 removal. Firstly, Pt-Re-Na/CeO2 and Pt-Re-Na/TiO2 catalysts were designed and prepared for WGS reaction. The effect of Na loading, support type, reaction temperature, feed type and composition (H2O/CO ratio) on WGS performance were considered as the experimental parameters. Among the prepared catalysts, sequentially impregnated 1%Pt-1%Re-2%Na/CeO2 exhibited the highest performance under Realistic Feed with H2O/CO=6.7. Serial OSR-WGS tests were also conducted for two OSR feed compositions having different O/C ratio and the highest real WGS activity was achieved over sequentially impregnated 1%Pt-1%Re-1%Na/CeO2 at 350°C as 43.0% CO conversion. The freshly reduced and spent forms of the catalyst samples were characterized by SEM, XPS, XRD and Raman spectroscopy. Combined evaluation of the Na1s and Ce3d spectra of the highly active catalysts, suggests the NaOx species should be more influential than CeOx species in the WGS reaction mechanisms. Surface formate and carbonate species under reaction conditions were examined in operando FTIR-DRIFTs-MS tests over Pt-Re-Na/CeO2 catalysts. The combined evaluation of WGS performance and OSC results indicated that structural OSC (S-OSC) and effective OSC (E-OSC) have both significant effect on WGS performance. E-OSC values of the catalysts were found in direct accordance with their performance results. In the adsorbent design part, CO2 and CH4 adsorption capacities of AC-based NaOH impregnated samples were determined for various “temperature-pressure range” couples, their selective adsorption capacities were measured under CO2-CH4 gas mixtures through using a novel methodology developed by our group, and the adsorption on the samples was modelled. The best performing adsorbent in terms of selective CO2 adsorption under CO2:CH4=1:1 and 1:9 was determined as AC6-200, which is the air oxidized AC doped with Na.