📚 IB and AQA Chemistry: Catalysis Exam Essentials | IB AQA 化学：催化 考点精讲
Catalysis sits at the heart of both IB and AQA chemistry syllabi, blending kinetics, thermodynamics and industrial applications. Understanding how catalysts work, the difference between homogeneous and heterogeneous pathways, and the ability to interpret energy profile diagrams are essential skills for top marks. This revision guide unpacks every key concept, from the basic definition to autocatalysis and catalytic converters, with paired English–Chinese explanations to reinforce your learning.
催化是 IB 和 AQA 化学课程的核心内容，融合了动力学、热力学和工业应用。理解催化剂的作用方式、均相与多相路径的区别，以及解读能量分布图的能力，是取得高分的必备技能。这份复习指南从基本定义到自催化和催化转化器，逐一剖析每个关键概念，并配以中英文对照解释，以强化你的学习。
1. Definition and Role of Catalysts | 催化剂的定义与作用
A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the overall process. It provides an alternative reaction pathway with a lower activation energy, Eₐ.
催化剂是一种能够加快化学反应速率而在总反应中不被消耗的物质。它通过提供一条活化能（Eₐ）较低的反应途径来发挥作用。
Catalysts do not alter the equilibrium constant, the enthalpy change (ΔH) or the equilibrium position; they accelerate both the forward and reverse reactions equally, so the system reaches equilibrium faster.
催化剂不改变平衡常数、焓变（ΔH）或平衡位置；它们同等程度地加速正反应和逆反应，因此体系能更快地达到平衡。
2. Catalysis and Activation Energy | 催化与活化能
A catalyst works by creating an alternative route where the energy barrier (Eₐ) is lower. It may stabilise a transition state or form reactive intermediates that require less energy to form.
催化剂的作用原理是创建一条能垒（Eₐ）较低的替代路径。它可以稳定过渡态，或者形成能量需求更低的活泼中间体。
According to the Maxwell– the fraction of molecules that have energy ≥ Eₐ, dramatically boosting the reaction rate.
根据麦克斯韦–玻尔兹曼分布，Eₐ 的微小降低会导致具备能量 ≥ Eₐ 的分子比例大幅增加，从而显著提高反应速率。
3. Energy Profile Diagrams | 能量分布图
An uncatalysed reaction shows a single energy hump whose height corresponds to Eₐ. For a catalysed reaction the hump is lower; if the mechanism involves a stable intermediate, the diagram displays two smaller humps separated by a trough.
未催化反应的能量分布图显示一个单峰，峰高对应 Eₐ。催化反应的能量分布图峰高降低；如果机理涉及稳定的中间体，图中会出现两个较小的峰，中间隔着一个凹谷。
Exam tip: always label ΔH and Eₐ on the diagram, and clearly indicate the catalysed versus uncatalysed pathway. The catalysed route must start and end at the same energy levels.
考试技巧：务必在图上标出 ΔH 和 Eₐ，并清晰区分催化与未催化路径。催化路径的起点和终点能量必须相同。
4. Homogeneous Catalysis | 均相催化
In homogeneous catalysis, the catalyst is in the same phase as the reactants, usually in solution. It often participates by forming an intermediate that regenerates the catalyst in a later step.
在均相催化中，催化剂与反应物处于同一相，通常为液相。催化剂常通过参与反应形成中间体，并在后续步骤中再生。
Classic example: the peroxodisulfate– : 2Fe³⁺ + 2I⁻ → I₂ + 2Fe²⁺, then 2Fe²⁺ + S₂O₈²⁻ → 2Fe³⁺ + 2SO₄²⁻. The Fe³⁺ is regenerated.
经典例子：过二硫酸根–碘离子反应。2I⁻ + S₂O₈²⁻ → I₂ + 2SO₄²⁻ 速率慢，但 Fe³⁺ 离子可催化：2Fe³⁺ + 2I⁻ → I₂ + 2Fe²⁺，随后 2Fe²⁺ + S₂O₈²⁻ → 2Fe³⁺ + 2SO₄²⁻，Fe³⁺ 得以再生。
Another AQA favourite is the oxidation of ethanedioate by acidified manganate(VII), autocatalysed by Mn²⁺, discussed later.
另一个 AQA 常见考点是酸化高锰酸钾氧化乙二酸根离子的反应，由 Mn²⁺ 自催化，稍后讨论。
5. Heterogeneous Catalysis and Adsorption | 多相催化与吸附
Heterogeneous catalysis involves a solid catalyst and gaseous or liquid reactants. Reaction occurs at the active sites on the surface after reactant molecules are adsorbed.
多相催化使用固体催化剂，反应物为气体或液体。反应物分子吸附在表面的活性位点上后发生反应。
Adsorption can be physisorption (weak van der Waals forces) or chemisorption (stronger bond formation). Chemisorption often weakens bonds inside the reactant molecules, lowering Eₐ.
吸附可分为物理吸附（弱的范德华力）或化学吸附（形成较强键）。化学吸附通常会削弱反应物分子内的键，从而降低 Eₐ。
After surface reaction, products desorb from the surface, freeing the active sites for another cycle. Transition metals (e.g. Ni, Pt, Fe) are excellent heterogeneous catalysts because of their variable oxidation states and partly filled d‑orbitals.
表面反应后，产物从表面解吸，释放出活性位点供下一个循环使用。过渡金属（如 Ni、Pt、Fe）因其可变氧化态和部分填充的 d 轨道，是极佳的多相催化剂。
6. Mechanisms of Catalysis | 催化机理
In homogeneous catalysis, the catalyst forms an intermediate; the overall activation energy is split into two smaller steps each with lower Eₐ. The catalyst appears unchanged at the end.
在均相催化中，催化剂形成中间体；总活化能被拆分为两个各具较低 Eₐ 的小步骤。最终催化剂表观不变。
In heterogeneous catalysis, the key steps are: (1) diffusion of reactants to the surface, (2) adsorption onto active sites, (3) reaction on the surface, (4) desorption of products, and (5) diffusion away. The rate-determining step is often the surface reaction or desorption.
多相催化的关键步骤为：(1) 反应物扩散至表面，(2) 吸附到活性位点，(3) 在表面反应，(4) 产物解吸，以及 (5) 扩散离开。决速步常为表面反应或解吸。
For AQA, you must be able to explain how V₂O₅ catalyses the Contact Process: step 1 – SO₂ + V₂O₅ → SO₃ + V₂O₄; step 2 – 2V₂O₄ + O₂ → 2V₂O₅. The catalyst is regenerated.
就 AQA 而言，你必须能解释 V₂O₅ 如何催化接触法：第一步 SO₂ + V₂O₅ → SO₃ + V₂O₄；第二步 2V₂O₄ + O₂ → 2V₂O₅。催化剂再生。
7. Enzymes as Biological Catalysts | 酶作为生物催化剂
Enzymes are globular proteins that function as highly specific biological catalysts. Their active site binds substrates, lowering Eₐ via acid–base, covalent or metal‑ion mechanisms.
酶是球状蛋白质，充当高度专一的生物催化剂。其活性位点结合底物，通过酸碱、共价或金属离子机理降低 Eₐ。
The lock‑and‑key and induced‑fit models explain substrate specificity. Enzyme activity is affected by temperature, pH and inhibitor molecules.
锁钥模型和诱导契合模型解释了底物专一性。酶活性受温度、pH 值和抑制剂分子的影响。
IB students may need to discuss Vmax and the Michaelis–Menten constant (Kₘ), while AQA focuses more on the effect of temperature and pH on the rate of enzyme‑catalysed reactions.
IB 学生可能需要讨论 Vmax 和米氏常数 (Kₘ)，而 AQA 更侧重于温度和 pH 对酶催化反应速率的影响。
8. Industrial Catalysis: Haber and Contact Processes | 工业催化：哈伯法与接触法
The Haber Process: N₂ + 3H₂ ⇌ 2NH₃, ΔH = –2 kJ mol⁻¹, uses a finely divided iron catalyst (Fe₃O₄ promoted with K₂O and Al₂O₃) at 400–450 °C and 200 atm. The catalyst dissociates N₂ and H₂ on its surface.
哈伯法：N₂ + 3H₂ ⇌ 2NH₃，ΔH = –92 kJ mol⁻¹，使用细碎的铁催化剂（Fe₃O₄ 以 K₂O 和 Al₂O₃ 为助催化剂），在 400–450 °C 和 200 atm 下，催化剂表面解离 N₂ 和 H₂。
The Contact Process: 2SO₂ + O₂ ⇌ 2SO₃ uses V₂O₅ as a catalyst. The mechanism involves redox cycling between V⁵⁺ and V⁴⁺ as shown in Section 6. Without the catalyst, the oxidation is impractically slow.
接触法：2SO₂ + O₂ ⇌ 2SO₃ 使用 V₂O₅ 作为催化剂。其机理涉及 V⁵⁺ 与 V⁴⁺ 之间的氧化还原循环，如第 6 节所示。若无催化剂，该氧化反应慢得毫无实际应用价值。
Both processes exemplify how a catalyst enables milder operating conditions and reduces energy costs, a key green‑chemistry benefit.
这两个工艺例证了催化剂如何令操作条件更温和、降低能耗，这正是绿色化学的核心优势。
9. Catalytic Converters and Green Chemistry | 催化转化器与绿色化学
Automotive catalytic converters contain a ceramic honeycomb coated with Pt, Pd and Rh. They catalyse the oxidation of CO and unburnt hydrocarbons to CO₂ and H₂O, and the reduction of NOₓ to N₂.
汽车催化转化器内含涂有 Pt、Pd 和 Rh 的陶瓷蜂窝载体。它们催化 CO 和未燃烧烃氧化为 CO₂ 和 H₂O，并将 NOₓ 还原为 N₂。
NO → 2CO₂ + N₂; CₓHᵧ + O₂ → CO₂ + H₂O. These devices reduce toxic emissions and are a real‑world application of heterogeneous catalysis.
典型反应：2CO + 2NO → 2CO₂ + N₂；CₓHᵧ + O₂ → CO₂ + H₂O。这些装置减少了有毒排放物，是多相催化的现实应用。
Catalysis aligns with the principles of Green Chemistry: it lowers energy requirements, reduces waste, and often permits the use of renewable feedstocks.
催化契合绿色化学的原则：它降低能量需求、减少废物，并常常允许使用可再生原料。
10. Autocatalysis, Poisoning and Exam Tips | 自催化、毒化与考试技巧
⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O. The produced Mn²⁺ ions catalyse the reaction, causing a sudden rate increase after an induction period.
在自催化中，反应产物之一充当催化剂。例如：乙二酸根与酸化高锰酸钾的反应：2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O。生成的 Mn²⁺ 离子催化该反应，导致经过诱导期后速率突然加快。
Catalyst poisoning occurs when impurities bind irreversibly to active sites, blocking the catalyst. Sulfur poisons the iron catalyst in the Haber process; lead poisons the catalytic converter. Regeneration or replacement is then required.
当杂质不可逆地结合到活性位点上时，催化剂便会毒化。硫会毒化哈伯法中的铁催化剂；铅会毒化催化转化器。此时需要再生或更换催化剂。
Exam strategies: always describe the alternative pathway with lower Eₐ, not that the catalyst “adds energy”. Draw energy profiles carefully, label Eₐ (cat) and Eₐ (uncat), and explain in terms of the Boltzmann distribution. For industrial processes, mention economic and environmental benefits. When given data, calculate the rate enhancement from Eₐ reductions using the Arrhenius equation when required.
考试策略：始终描述具有较低 Eₐ 的替代路径，而不要说催化剂“提供能量”。仔细绘制能量分布图，标出 Eₐ(催化) 和 Eₐ(非催化)，并用玻尔兹曼分布进行解释。对于工业流程，要提及经济和环境效益。给出数据时，若需要应利用阿伦尼乌斯公式从 Eₐ 的降低计算速率提升倍数。
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