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Sorption enhanced steam reforming of biogas is a promising process for H 2 production by which biogas steam reforming is combined with simultaneous CO 2 capture in a single unit operation. In the first part, Zr 4+ , Ce 4+ and La 3+ were doped on CaO and tested the performance for 10 CO 2 sorption/desorption cycles. Zr-CaO and Ce-CaO offered a stable CO 2 capture activity for at least 10 cycles (CO 2 sorption capacity of 0.30 and 0.22 g CO 2 / g sorbent at the 1st cycle, and 0.29 and 0.23 g CO 2 / g sorbent at the 10th cycle for Zr-CaO and Ce-CaO, respectively). On the other hand, La-CaO indicated decreasing of CO 2 sorption capacity about 16% over 10 cycle operations. This is due to the Zr-CaO and Ce-CaO presented oxygen storage at low temperature which is characterized by temperature program reduction oxidation (TPRO). This behavior promotes the CO 2 diffusion from the surface to the bulk (sorption) and the bulk to the surface (desorption) of the modified CaO. In the second part, Ni 2+ was loaded on the modified sorbents for H 2 production. Ni-Zr-CaO and Ni-Ce-CaO can enable the production of H 2 with purities of approximately 90% and 85%, respectively, with repeating cycles; however, the CH 4 conversions decreased significantly over five cycles (the post-breakthrough period CH 4 conversion of Ni-Zr-CaO and Ni-Ce-CaO decreased from 65.6 and 56.3% during the 1st cycle to 33.0 and 28.9% during the 5th cycle). This is because the Ni active sites at the surface of multifunctional catalysts were lost (as confirmed by XPS results) by pore closure (as shown in SEM images) which was possibly due to the CaCO 3 formation. [ABSTRACT FROM AUTHOR]

Modified sorbents (NiO CaO and Ca 12 Al 14 O 33 CaO) were synthesized by hydration followed by wet mixing (HW) and tested in terms of their CO 2 sorption/desorption performance over multiple cycles. The results indicated the sorption capacities for Ni–CaO-HW and Al–CaO-HW decreased by only 3.8% and 6.4%, respectively, over 10 cycles. Various sequences of Ni 2+ loading onto modified CaO were investigated. The results indicated Ni–Al–CaO-HW to be the best performing exhibiting a pre-breakthrough time 30 min longer than the other samples. However, the H 2 purity and CH 4 conversion did not differ significantly amongst the various sorbents (approx. 94% purity H 2 and approx. 90% CH 4 conversion pre-breakthrough). The stability of the Ni–Al–CaO-HW was also investigated and the results indicated that the pre-breakthrough CH 4 conversion could be maintained at steady values for five cycles. However, the post-breakthrough CH 4 conversion decreases slightly over five cycles. A plausible explanation is that the formation of CaCO 3 results in the blockage of pores and active sites, which is supported by XPS results. [ABSTRACT FROM AUTHOR]