Metal oxide‐doped Ni/CaO dual‐function materials for integrated CO₂ capture and conversion: Performance and mechanism

Abstract

Integrated CO2 capture and conversion (ICCC) into valuable chemicals such as CH4 and CO is a promising approach to mitigate anthropogenic CO2 emissions. In this work, we prepared a series of metal oxide (MxOy, M = Mg, Al, Mn, Y, Zr, La, and Ce)‐doped Ni/CaO dual‐function materials (DFMs) and applied them to the ICCC process. The property–performance relationship of the DFMs was studied, and the conversion mechanism of the captured CO2 was explored. For any DFM at any ICCC cycle (20 cycles in total), the CO2 captured at the carbonation stage was completely released as CH4, CO, and CO2 at the conversion stage. Among all DFMs, Ni/CaZr(O) showed the best ICCC performance because of its good thermal stability. The conversion of captured CO2 on the DFMs proceeded via a two‐step mechanism, where CO2 was first released from CaCO3 and then converted into CH4 at Ni sites and CO at CaO sites.

Application of engineered natural ores to intermediate‐ and high‐temperature CO2 capture and conversion

“…At the stage of CO 2 capture (i.e., the first step mentioned above), the outlet flow rate of CO 2 was monitored in real time by Vaisala GMP251 CO 2 probe. The CO 2 uptake of sorbents at any time () is calculated by subtracting the dead volume of the ICCC system as follows 18 : where m 0 is the initial weight of sorbents in the reactor, and and represent the outlet molar flow rates of CO 2 in blank and actual tests, respectively. The blank experiment was conducted using inert quartz sand under the working condition.…”

“…The inlet gas flow rates were adjusted by mass flow meters, and the reaction temperature was controlled by a three- At the stage of CO 2 capture (i.e., the first step mentioned above), the outlet flow rate of CO 2 was monitored in real time by Vaisala GMP251 CO 2 probe. The CO 2 uptake of sorbents at any time (q CO2 ) is calculated by subtracting the dead volume of the ICCC system as follows 18 :…”

“…Sorbent and catalyst can be separated as two particles in a reactor, or integrated into one particle (i.e., so‐called dual‐function materials, DFMs) 12–14 . The DFMs have the advantage of enhanced mass and heat transfer between adsorptive and catalytic sites due to their close proximity to each other, providing an additional degree of freedom for reactor design 15–19 . However, in order to achieve DFMs with remarkable CO 2 capture capacity, high catalytic activity and product selectivity as well as good cyclic stability, the adsorptive and catalytic sites need to be fine‐tuned, which inevitably increases the complexity in design and manufacturing of DFMs.…”

“…[12][13][14] The DFMs have the advantage of enhanced mass and heat transfer between adsorptive and catalytic sites due to their close proximity to each other, providing an additional degree of freedom for reactor design. [15][16][17][18][19] However, in order to achieve DFMs with remarkable CO 2 capture capacity, high catalytic activity and product selectivity as well as good cyclic stability, the adsorptive and catalytic sites need to be fine-tuned, which inevitably increases the complexity in design and manufacturing of DFMs. By contrast, the two-particle configuration has the advantages of low complexity and easy realization because sorbent and catalyst particles can be optimized separately, especially in the context of great progress in the catalysts for CO 2 conversion in recent years.…”

Synergistic promotions of K doping on CO2 capture and in situ conversion

“…Among them, CaO-based DFMs are the most investigated and applied due to their high CO 2 capture capacity, low cost, and abundant resources. [7][8][9][10][11] However, the high operating temperature above 700 C not only aggravates the sintering of sorbents and catalysts, 12 but also makes it more costly and challenging for large-scale industrial deployments due to the strict heat-resistant requirements for the installation materials, the high energy consumption, and the safety issues. 5,[13][14][15] In contrast, the alkaline ceramic materials, such as Li 4 SiO 4 through the lithium-looping (LiL, Li 4 SiO 4 + CO 2 $ Li 2 SiO 3 + Li 2 CO 3 ), [16][17][18][19] exhibit a high CO 2 capture capability and excellent cycle stability in a relatively lower temperature range of 500-600 C. [20][21][22][23] To match this CO 2 capture temperature, the revised water gas shift (RWGS) reaction can be a more promising choice than the dry reforming of methane (700-800 C) and CO 2 methanation (300-400 C) for the in situ CO 2 conversion.…”