I.CO2(g)+H2(g)CO(g)+H2O(g) △H1=+41kJ·mol-1
II.CO2(g)+4H2(g)CH4(g)+2H2O(g) △H2
III.CO2(g)+CH4(g)2CO(g)+2H2(g) △H3=+247kJ·mol-1