Simultaneous CO2 adsorption and conversion over Ni-Pd supported CeO2 nanoparticles during catalytic n-C7 asphaltene gasification

Abstract

Shallow heavy oil reservoirs are suitable for the geo-sequestration of CO2 based on its adsorption and conversion during thermal-enhanced oil recovery processes. This study aims to evaluate multifunctional nanomaterials for CO2 adsorption and its subsequent transformation into valuable sub-products during the catalytic decomposition of asphaltenes in a steam gasification atmosphere. Three ceria nanoparticles with cubic (C-CeO2), orthorhombic (O-CeO2), and spherical (S-CeO2) shapes were tested in four stages including i) CO2 adsorption at 30, 50, 100, and 200 °C between 0.084 and 3.0 MPa, ii) dynamic in-situ CO2 adsorption in the presence of steam between 170 and 230 °C at 3.0 MPa, iii) dynamic in-situ CO2 adsorption in the presence of steam with adsorbed asphaltenes between 170 and 230 °C at 3.0 MPa and iv) CO2 conversion at the same conditions. The best nanoparticle morphology was doped with 1 wt% of Ni and Pd (C-CeNiPd) and was tested in the same experiments. Among the most important results, CO2 adsorption increased in the order S-CeO2 < O-CeO2 < C-CeO2 < C-CeNiPd, regardless of the temperature. When steam was injected, CO2 adsorption is reduced in all the systems. At 200 °C adsorption decreased by 3.0 %, 2.7 %, 2.5 %, and 2.0 % in processes assisted by S-CeO2, O-CeO2, C-CeO2, and C-CeNiPd, respectively. Nanoparticles with adsorbed asphaltenes presented a high tendency for CO2 adsorption as well. The nanoparticle with the best morphology (C-CeO2) adsorbed about 24.3 % (3.92 mmol) of CO2 at 200 °C, and the yield increased after doping with Ni and Pd, obtaining CO2 adsorption of 34 %. Finally, for CO2 conversion, a mixture of gases composed of CO, CH4, H2, and light hydrocarbons (LHC) is obtained. The hydrogen production content follows a trend that agrees well with each material's adsorptive capacity and catalytic activity. The maximum %vol of H2 produced at 200 °C during asphaltene gasification was 31 %, 29 %, 24 %, and 23 % for C-CeNiPd, C-CeO2, O-CeO2, and S-CeO2, respectively.