CO methanation reaction over the Ni/Al2O3 catalysts for synthetic natural gas production was systematically
investigated by tuning a number of parameters, including using different
commercial Al2O3 supports and varying NiO and
MgO loading, calcination temperature, space velocity, H2/CO ratio, reaction pressure, and time, respectively. The catalytic
performance was greatly influenced by the above-mentioned parameters.
Briefly, a large surface area of the Al2O3 support,
a moderate interaction between Ni and the support Al2O3, a proper Ni content (20 wt %), and a relatively low calcination
temperature (400 °C) promoted the formation of small NiO particles
and reducible β-type NiO species, which led to high catalytic
activities and strong resistance to the carbon deposition, while addition
of a small amount of MgO (2 wt %) could improve the catalyst stability
by reducing the carbon deposition; other optimized conditions that
enhanced the catalytic performance included high reaction pressure
(3.0 MPa), high H2/CO ratio (≥3:1), low space velocity,
and addition of quartz sand as the diluting agent in catalyst bed.
The best catalyst combination was 20–40 wt % of NiO supported
on a commercial Al2O3 (S4) with addition
of 2–4 wt % of MgO, calcined at 400–500 °C and
run at a reaction pressure of 3.0 MPa. On this catalyst, 100% of CO
conversion could be achieved within a wide range of reaction temperature
(300–550 °C), and the CH4 selectivity increased
with increasing temperature and reached 96.5% at a relatively low
temperature of 350 °C. These results will be very helpful to
develop highly efficient Ni-based catalysts for the methanation reaction,
to optimize the reaction process, and to better understand the above
reaction.
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