複選題

27. There are three methods for hydrogen production

(1) Methane pyrolysis:
$\mathrm{CH_4(g)} \rightarrow \mathrm{C(s)} + 2 \mathrm{H_2(g)}$; $\Delta \mathrm{H} = +76 \mathrm{kJ}$, corresponding to $+38 \mathrm{kJ}$ per mole of $\mathrm{H_2}$ produced.

(2) Water electrolysis:
$2 \mathrm{H_2O(l)} \rightarrow \mathrm{O_2(g)} + 2 \mathrm{H_2(g)}$; $\Delta \mathrm{H} = +572 \mathrm{kJ}$, corresponding to $+286 \mathrm{kJ}$ per mole of $\mathrm{H_2}$ produced.

(3) Steam methane reforming:
$\mathrm{CH_4(g)} + 2 \mathrm{H_2O(g)} \rightarrow \mathrm{CO_2(g)} + 4 \mathrm{H_2(g)}$; $\Delta \mathrm{H} = +252 \mathrm{kJ}$, corresponding to $+63 \mathrm{kJ}$ per mole of $\mathrm{H_2}$ produced.

Based solely on the reaction enthalpies $(\Delta \mathrm{H})$, methane pyrolysis [method (1)] appears to be the most energy-efficient pathway for hydrogen production. However, this conclusion is misleading in practice and does not adequately represent the true energetic and technological challenges of the process. Which of the following statements correctly explain the reasons?
(A) Although the net enthalpy requirement is only $38\mathrm{kJ}$ per mole of $\mathrm{H}_{2}$, a much higher activation energy must be overcome to cleave the strong C-H bonds in methane.
(B) Non-catalytic methane pyrolysis requires temperatures above approximately $1200^{\circ}\mathrm{C}$, with activation energies typically in the range of $300 - 420\mathrm{kJ / mol}$.
(C) Catalytic methane pyrolysis employing metal (e.g., Ni, Fe, Cu) or carbon catalysts can lower the required operating temperature to approximately $600 - 900^{\circ}\mathrm{C}$ and reduce the activation energy to about $150 - 200\mathrm{kJ / mol}$.
(D) In methane pyrolysis reactors, heat transfer to methane is generally less efficient than in steam methane reforming [method (3)], which benefits from the use of high-temperature water vapor as an effective heat-transfer medium.


(E) In [method 3], the total bond enthalpy of the products is less than that of reactants.