Catalysis for CCEA A-Level Chemistry | A-Level CCEA 化学：催化考点精讲

📚 Catalysis for CCEA A-Level Chemistry | A-Level CCEA 化学：催化考点精讲

Catalysis is a cornerstone topic in CCEA A-Level Chemistry, linking kinetics, industrial processes, and green chemistry. A catalyst is a substance that increases the rate of a chemical reaction without being permanently changed itself. This article covers the core principles of catalysis, including homogeneous and heterogeneous systems, activation energy profiles, and key industrial and biological examples. Written to align with the CCEA specification, it provides clear explanations, reaction mechanisms, and practice-oriented insights to help you master the essentials of catalytic action.

催化是 CCEA A-Level 化学中的一个核心主题，它将动力学、工业流程与绿色化学联系在一起。催化剂是一种能够提高化学反应速率而自身不发生永久性变化的物质。本文涵盖了催化的基本原理，包括均相与多相催化体系、活化能曲线图以及重要的工业与生物学实例。文章严格依据 CCEA 考纲编写，提供清晰的解释、反应机理和面向考试的要领，帮助你掌握催化作用的精髓。

1. Defining Catalysts and Their Key Characteristics | 催化剂的定义及主要特征

A catalyst is a substance that speeds up a chemical reaction without undergoing any permanent chemical change itself. It achieves this by providing an alternative reaction pathway with a lower activation energy, Eₐ. Importantly, a catalyst does not alter the enthalpy change (ΔH) of the reaction, nor does it affect the position of equilibrium; it merely allows equilibrium to be reached more quickly by lowering the energy barrier for both the forward and reverse reactions equally.

催化剂是一种能加快化学反应速率而自身不发生永久性化学变化的物质。它通过提供具有较低活化能 Eₐ 的替代反应路径来实现这一点。重要的是，催化剂不会改变反应的焓变 ΔH，也不会影响平衡位置；它只是同等地降低正反应和逆反应的能量壁垒，从而使平衡更快到达。

At a particulate level, catalysts work by enabling a different sequence of bond-breaking and bond-making steps, often involving the formation of intermediate species. These intermediates are subsequently converted back to the free catalyst, which can then participate in another catalytic cycle. This regenerability is the reason a small amount of catalyst can process a large quantity of reactant.

在微粒层面，催化剂通过促成不同的断键与成键步骤序列来发挥作用，这些步骤通常涉及中间物种的生成。这些中间体随后被转化回游离的催化剂，使催化剂能够参与下一次循环。这种再生能力正是少量催化剂即可处理大量反应物的原因。

The requirements for a catalytic reaction are thus: (i) the catalyst must be present in at least one step of the mechanism; (ii) it must be regenerated in a later step; and (iii) the overall energy profile must show a lower Eₐ compared to the uncatalysed route. In rate–concentration graphs, the presence of a catalyst produces a steeper gradient without altering the final extent of reaction.

因此，催化反应需要满足：(i) 催化剂必须出现在机理的至少一个步骤中；(ii) 它必须在后续步骤中被再生；(iii) 与非催化路径相比，总能量曲线图必须显示出更低的 Eₐ。在速率–浓度图中，催化剂的存在会使曲线初始斜率更陡，但不改变反应的最终程度。

2. Activation Energy and Reaction Profiles | 活化能与反应能量图

The concept of activation energy is central to understanding catalysis. In an uncatalysed reaction, the reactants must surmount a relatively high energy barrier before being converted into products. When a catalyst is introduced, the reaction proceeds via an alternative transition state (or a series of transition states) of lower energy, thereby reducing Eₐ. This means a greater fraction of reactant molecules possess sufficient energy to react at a given temperature, as described by the Maxwell–Boltzmann distribution.

活化能的概念是理解催化的关键。在非催化反应中，反应物必须越过一个相对较高的能量壁垒才能转化为产物。当加入催化剂后，反应通过能量较低的另一过渡态（或一系列过渡态）进行，从而降低 Eₐ。这意味着在给定温度下，具有足够能量发生反应的反应物分子比例增大，正如麦克斯韦–玻尔兹曼分布所描述的那样。

On a reaction profile diagram, the uncatalysed pathway shows a single high peak. The catalysed route appears as a profile with a lower peak, or possibly two smaller peaks if a distinct intermediate is formed. For the CCEA examination, you should be able to sketch such profiles, labelling the enthalpy change (ΔH), activation energies for forward and reverse reactions (Eₐ(fwd) and Eₐ(rev)) with and without a catalyst, and clearly indicate that ΔH remains unchanged.

在反应路径图中，非催化路径显示为一个高的单峰。催化路径则表现为峰高较低，若生成明显的中间体，还可能出现两个较小的峰。在 CCEA 考试中，你需要能够绘制此类能量图，并标注焓变 ΔH、有催化剂和无催化剂时的正、逆反应活化能 Eₐ(正) 和 Eₐ(逆)，并且明确指出 ΔH 保持不变。

Because Eₐ(rev) is also lowered by a catalyst, the reverse reaction is accelerated to the same extent as the forward reaction. This is why a catalyst does not change the equilibrium constant K꜀ or the equilibrium composition—only the time taken to achieve equilibrium is reduced. Questions often ask you to calculate or compare the proportion of molecules exceeding Eₐ using the Arrhenius equation; a lower Eₐ drastically increases the rate constant k.

由于催化剂同样降低了逆反应的活化能 Eₐ(逆)，逆反应与正反应被同等程度地加速。这就是催化剂不改变平衡常数 K꜀ 或平衡组成的原因——它仅仅缩短了达到平衡所需的时间。考题常要求使用阿伦尼乌斯方程计算或比较超过 Eₐ 的分子比例；较低的 Eₐ 会显著增大速率常数 k。

3. Homogeneous Catalysis | 均相催化

Homogeneous catalysis occurs when the catalyst and the reactants are in the same physical state, most commonly in the liquid or gas phase. A classic example studied in CCEA Chemistry is the catalysis of the reaction between iodide ions and peroxodisulfate ions by iron(II)/iron(III) ions. The overall equation is: 2I⁻ + S₂O₈²⁻ → I₂ + 2SO₄²⁻. This reaction is slow in the absence of a catalyst because both ions are negatively charged and repel each other.

当催化剂与反应物处于同一物理状态（通常为液相或气相）时，即为均相催化。CCEA 化学课程中学习的一个经典例子是铁(II)/铁(III)离子催化碘离子与过二硫酸根离子之间的反应。总反应方程式为：2I⁻ + S₂O₈²⁻ → I₂ + 2SO₄²⁻。若无催化剂，该反应很慢，因为两种离子均带负电荷并相互排斥。

The Fe²⁺/Fe³⁺ catalyst works via two fast steps. Step 1: S₂O₈²⁻ oxidises Fe²⁺ to Fe³⁺: 2Fe²⁺ + S₂O₈²⁻ → 2Fe³⁺ + 2SO₄²⁻. Step 2: Fe³⁺ oxidises I⁻ to I₂, regenerating Fe²⁺: 2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂. The Fe²⁺ is consumed in the first step and regenerated in the second, so it qualifies as a true catalyst. The activation energy is lowered because the two-step mechanism avoids the direct collision of two large negative ions.

Fe²⁺/Fe³⁺ 催化剂通过两个快步骤发挥作用。第一步：S₂O₈²⁻ 将 Fe²⁺ 氧化为 Fe³⁺：2Fe²⁺ + S₂O₈²⁻ → 2Fe³⁺ + 2SO₄²⁻。第二步：Fe³⁺ 将 I⁻ 氧化为 I₂，同时再生 Fe²⁺：2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂。Fe²⁺ 在第一步中被消耗，在第二步中再生，因此是真正的催化剂。该两步机理避免了两个大型负离子的直接碰撞，从而降低了活化能。

Another important homogeneous system is acid-catalysed ester hydrolysis, where H⁺ ions protonate the carbonyl oxygen, making the carbon more electrophilic and susceptible to nucleophilic attack by water. In the gas phase, chlorine radicals Cl• catalyse the decomposition of ozone in the stratosphere: Cl• + O₃ → ClO• + O₂; ClO• + O → Cl• + O₂. Although radical-based, this is a homogeneous catalytic cycle and is explicitly mentioned in many specification-linked resources.

另一个重要的均相催化体系是酸催化的酯水解，其中 H⁺ 离子质子化羰基氧，使碳更具亲电性，易受水分子的亲核进攻。在气相中，氯自由基 Cl• 催化平流层中臭氧的分解：Cl• + O₃ → ClO• + O₂；ClO• + O → Cl• + O₂。虽然涉及自由基，但这属于均相催化循环，许多与考纲配套的资料中均有明确提及。

4. Heterogeneous Catalysis and Adsorption Theory | 多相催化与吸附理论

Heterogeneous catalysis involves a catalyst in a different phase from the reactants; typically a solid catalyst with gaseous or liquid reactants. The reaction takes place on the surface of the solid. The process can be broken down into three essential stages: (1) adsorption of reactant molecules onto active sites on the catalyst surface, (2) reaction between adsorbed species to form products, and (3) desorption of product molecules, which frees the active sites for further catalytic cycles.

多相催化中，催化剂与反应物处于不同的相；典型的例子是固体催化剂与气态或液态反应物之间的反应。反应发生在固体表面上。该过程可分解为三个基本阶段：(1) 反应物分子吸附到催化剂表面的活性位点上；(2) 被吸附的物种在表面发生反应生成产物；(3) 产物分子解吸，从而释放出活性位点以进行下一轮催化循环。

Adsorption can be physisorption (weak van der Waals forces) or chemisorption (actual chemical bonds formed between adsorbate and surface atoms). Effective heterogeneous catalysts often rely on chemisorption that is strong enough to weaken bonds within the reactant molecules, but not so strong that the products cannot desorb. Transition metals are frequently used because of their partially filled d-orbitals, which allow them to form temporary bonds with reactant molecules.

吸附可分为物理吸附（弱的范德华力）和化学吸附（吸附质与表面原子间形成真正的化学键）。高效的多相催化剂通常依赖强度适中的化学吸附：足以削弱反应物分子内部的化学键，但又不会强到使产物无法解吸。过渡金属因其部分填充的 d 轨道能够与反应物分子形成临时化学键而常被用作催化剂。

Students should appreciate how increasing the surface area of a solid catalyst—for example by using a finely divided metal or a porous support—greatly enhances catalytic activity because more active sites are exposed. Poisoning, discussed later, occurs when an impurity binds irreversibly to these sites, permanently blocking them.

学生应理解，增大固体催化剂的表面积（例如使用细分散金属或多孔载体）可大幅提高催化活性，因为暴露了更多的活性位点。后面将讨论的催化剂中毒正是由于杂质不可逆地结合在这些位点上并将其永久堵塞所致。

5. Industrial Catalysis: The Haber Process | 工业催化：哈柏法

The Haber process for ammonia synthesis is one of the most important heterogeneously catalysed reactions in the world. The overall reaction is N₂(g) + 3H₂(g) ⇌ 2NH₃(g), with ΔH = −92 kJ mol⁻¹. The catalyst is finely divided iron (often promoted with potassium oxide and aluminium oxide to enhance activity and stability). Typical operating conditions are around 400–450 °C and 200 atm, chosen as a compromise between rate, yield, and economic factors.

哈柏法合成氨是世界上最重要的多相催化反应之一。总反应为 N₂(气) + 3H₂(气) ⇌ 2NH₃(气)，ΔH = −92 kJ mol⁻¹。催化剂为细分散的铁（通常用氧化钾和氧化铝作为促进剂以提高活性和稳定性）。典型操作条件约为 400–450 °C 和 200 个大气压，这是在反应速率、产率和经济因素之间折衷的结果。

The mechanism on the iron surface involves dissociative chemisorption: N₂ molecules are adsorbed and their strong N≡N triple bond is broken, forming separate nitrogen atoms bound to the surface. Hydrogen molecules also adsorb and dissociate into H atoms. Stepwise hydrogenation of surface nitrogen atoms yields NH, then NH₂, and finally NH₃, which desorbs from the surface. The rate-determining step is generally the initial dissociation of N₂, which is why a catalyst that can weaken the N≡N bond is essential.

铁表面上的机理涉及解离化学吸附：N₂ 分子被吸附后，其牢固的 N≡N 三键断裂，形成结合在表面上的独立氮原子。氢分子同样吸附并解离为 H 原子。表面氮原子逐步加氢依次生成 NH、NH₂，最终生成 NH₃，后者从表面解吸。决速步骤通常是 N₂ 的初始解离，因此能够削弱 N≡N 键的催化剂至关重要。

The iron catalyst is susceptible to poisoning by sulfur compounds and arsenic impurities in the feedstock; these bind strongly to the active sites and deactivate the catalyst. Hence the reactants must be thoroughly purified before entering the reactor. Understanding these practical details is frequently tested in CCEA questions that link kinetics with industrial chemistry.

铁催化剂易被原料气中的硫化物和砷杂质中毒；这些杂质与活性位点牢固结合，使催化剂失活。因此反应物在进入反应器前必须彻底净化。这些实际细节常出现在 CCEA 考题中，将动力学与工业化学联系起来。

6. Industrial Catalysis: The Contact Process | 工业催化：接触法

The Contact process produces sulfuric acid, the world’s most manufactured chemical. The key catalysed step is the oxidation of sulfur dioxide: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH = −197 kJ mol⁻¹. The catalyst is vanadium(V) oxide, V₂O₅, supported on a porous silica material to maximise surface area. The reaction operates at around 400–450 °C and 1–2 atm, as the equilibrium already strongly favours SO₃ at low temperatures, but a higher temperature is required to achieve an acceptable rate.

接触法生产硫酸——全球产量最大的化学品。关键的催化步骤是二氧化硫的氧化：2SO₂(气) + O₂(气) ⇌ 2SO₃(气)，ΔH = −197 kJ mol⁻¹。催化剂为负载在多孔二氧化硅上的五氧化二钒 V₂O₅，以最大化表面积。反应在约 400–450 °C 和 1–2 个大气压下进行，因为尽管低温下平衡强烈倾向于生成 SO₃，但仍需较高温度以获得可接受的速率。

Importantly, V₂O₅ does not simply provide a surface—it actually participates in a redox cycle. In the first step, V₂O₅ oxidises SO₂ to SO₃ and is itself reduced to V₂O₄: V₂O₅ + SO₂ → V₂O₄ + SO₃. In the second step, V₂O₄ is re-oxidised by oxygen back to V₂O₅: 2V₂O₄ + O₂ → 2V₂O₅. The overall equation is the sum of these two steps, and V₂O₅ emerges unchanged. This makes the catalyst effectively a homogeneous player within a heterogeneous system at the surface layer.

重要的是，V₂O₅ 并非仅仅提供表面——它实际上参与了氧化还原循环。第一步中，V₂O₅ 将 SO₂ 氧化为 SO₃，自身被还原为 V₂O₄：V₂O₅ + SO₂ → V₂O₄ + SO₃。第二步中，V₂O₄ 被氧气重新氧化为 V₂O₅：2V₂O₄ + O₂ → 2V₂O₅。总反应为这两步之和，V₂O₅ 最终保持不变。这使得该催化剂实质上在多相体系中充当了表层均相参与者的角色。

The Contact process is relatively resistant to poisoning, but dust and arsenic impurities can still reduce catalyst life. Modern plants use multiple catalyst beds and inter-stage cooling to optimise conversion, reaching over 99.5% yield of SO₃. Examiners often ask you to explain why a lower temperature cannot be used despite the exothermic nature, or to write the redox equations for the V₂O₅ cycle.

接触法对中毒有较强抵抗力，但粉尘和砷杂质仍会缩短催化剂寿命。现代工厂采用多段催化床和段间冷却来优化转化率，SO₃ 产率可达 99.5% 以上。考官常会问及：既然反应放热，为何不能采用更低的温度；或者要求写出 V₂O₅ 氧化还原循环的方程式。

7. Enzymes: Biological Catalysts | 酶：生物催化剂

Enzymes are globular proteins that act as highly specific biological catalysts. They increase the rates of biochemical reactions by factors of millions, operating under mild conditions of temperature and pH. The substrate binds to the enzyme’s active site—a region with a unique three-dimensional shape—to form an enzyme–substrate complex. This binding stabilises the transition state and lowers the activation energy dramatically.

酶是球状蛋白，作为高度专一的生物催化剂发挥作用。它们能在温和的温度和 pH 条件下将生化反应速率提高数百万倍。底物与酶的活性位点（具有独特三维形状的区域）结合，形成酶–底物复合物。这种结合稳定了过渡态，并显著降低活化能。

Two models describe enzyme specificity: the ‘lock-and-key’ model assumes a rigid active site exactly complementary to the substrate; the ‘induced-fit’ model, which is more accurate, proposes that the active site changes shape slightly upon substrate binding to achieve an optimal fit. In either case, the exquisite specificity arises from the precise arrangement of amino acid side chains forming hydrogen bonds, ionic interactions, and hydrophobic pockets.

两种模型可用于描述酶的专一性：“锁钥”模型假设活性位点与底物刚性互补；“诱导契合”模型更为准确，认为活性位点在底物结合时发生轻微形变以实现最佳契合。无论哪种模型，其精妙的专一性均源于氨基酸侧链的精确排布所形成的氢键、离子相互作用和疏水口袋。

Enzyme activity is influenced by temperature and pH. As temperature rises, the rate initially increases in line with kinetic theory, but beyond an optimum (often around 37–40 °C for human enzymes), the protein denatures and the activity plummets. Similarly, each enzyme has an optimal pH; deviations alter the ionisation of active-site residues, disrupting substrate binding. Competitive and non-competitive inhibitors also feature in CCEA specifications and are compared in terms of their binding sites and effects on Vₘₐₓ and Kₘ.

酶活性受温度和 pH 的影响。随着温度升高，速率起初按动力学理论增加，但超过最适温度（人体酶通常为 37–40 °C）后，蛋白质变性，活性骤降。类似地，每种酶都有其最适 pH；偏离该值会改变活性位点残基的电离状态，从而破坏底物结合。CCEA 考纲还涉及竞争性与非竞争性抑制剂，需要比较它们的结合位点以及对 Vₘₐₓ 和 Kₘ 的影响。

8. Catalytic Converters in Automobiles | 汽车催化转化器

Catalytic converters fitted in vehicle exhaust systems reduce harmful emissions. They consist of a ceramic honeycomb monolith coated with a high-surface-area washcoat containing platinum, palladium, and rhodium as catalysts. The honeycomb structure provides a large surface area while allowing exhaust gases to flow through with minimal back pressure.

安装在汽车排气系统中的催化转化器可减少有害排放。它由一个陶瓷蜂窝状整块载体构成，载体上涂覆有高表面积的涂层，内含铂、钯和铑作为催化剂。蜂窝结构提供了巨大的表面积，同时允许废气以最低背压流过。

Two main types of reactions occur: oxidation of carbon monoxide and unburnt hydrocarbons to CO₂ and H₂O, and reduction of nitrogen oxides (NOₓ) to N₂. For example: 2CO + O₂ → 2CO₂; CₓHᵧ + (x + y/4)O₂ → xCO₂ + (y/2)H₂O; 2CO + 2NO → 2CO₂ + N₂. Rhodium is particularly effective for NOₓ reduction, while platinum and palladium excel in oxidation reactions. Modern three-way catalytic converters simultaneously perform both oxidation and reduction, hence the name.

发生两类主要反应：一氧化碳和未燃烧烃类的氧化（生成 CO₂ 和 H₂O），以及氮氧化物 NOₓ 的还原（生成 N₂）。例如：2CO + O₂ → 2CO₂；CₓHᵧ + (x + y/4)O₂ → xCO₂ + (y/2)H₂O；2CO + 2NO → 2CO₂ + N₂。铑对 NOₓ 还原尤为有效，而铂和钯则擅长氧化反应。现代三元催化转化器可同时进行氧化与还原反应，故得此名。

Catalytic converters require a stoichiometric air-to-fuel ratio and are rendered inactive by lead compounds, which irreversibly poison the precious metal sites. Consequently, vehicles fitted with catalytic converters must use unleaded fuel. CCEA examiners frequently link this topic with environmental chemistry and the properties of transition metals.

催化转化器需要化学计量比的空燃比，并且会因铅化合物而失活——铅不可逆地毒化贵金属活性位点。因此，装有催化转化器的车辆必须使用无铅汽油。CCEA 考官常将这一主题与环境化学及过渡金属的性质相结合进行考查。

9. Autocatalysis | 自催化

Autocatalysis is a special case in which one of the reaction products functions as the catalyst. The reaction starts slowly, but as catalyst molecules are produced, the rate accelerates until the reactants are significantly depleted. A characteristic observation is an induction period followed by a rapid increase in rate, producing an S-shaped (sigmoidal) concentration–time curve for the product.

自催化是一种特殊情况，即反应产物之一充当催化剂。反应开始时很慢，但随着催化剂分子的生成，速率加快，直至反应物被大量消耗。典型的实验现象是先有一个诱导期，随后速率迅速上升，产物的浓度–时间曲线呈 S 形（西格摩德形）。

The most common example examined at A-Level is the reaction between acidified potassium manganate(VII) and ethanedioic acid (or ethanedioate ions). The equation: 2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O. The Mn²⁺ ions produced catalyse the reaction. Initially the purple colour fades very slowly; once a sufficient concentration of Mn²⁺ builds up, the decolorisation becomes rapid. Warming the mixture is sometimes required to initiate the reaction.

A-Level 阶段最具代表性的例子是酸化高锰酸钾与乙二酸（或乙二酸根离子）的反应。方程式为：2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O。反应生成的 Mn²⁺ 离子起催化作用。开始时紫色褪去非常缓慢；一旦 Mn²⁺ 达到足够浓度，褪色便骤然加快。有时需要微热混合物以启动反应。

Another example, sometimes referenced in extension, is the reaction of copper with dilute nitric acid, where nitrous acid or NO acts autocatalytically. In the laboratory, the manganese system provides an excellent demonstration of the effect of increasing catalyst concentration on rate, and you may be asked to sketch the rate curve and explain the shape in terms of the catalytic cycle involving Mn²⁺/Mn³⁺ intermediate steps.

另一个有时提及的例子是铜与稀硝酸的反应，其中亚硝酸或 NO 起自催化作用。在实验室中，锰体系极好地展示了催化剂浓度对速率的影响；你可能被要求绘制速率曲线，并用涉及 Mn²⁺/Mn³⁺ 中间步骤的催化循环来解释曲线形状。

10. Catalyst Poisoning and Deactivation | 催化剂中毒与失活

Catalyst poisoning occurs when a foreign substance binds very strongly—often irreversibly—to the active sites of a catalyst, preventing reactant molecules from accessing them. Even trace amounts of poison can drastically reduce catalytic activity, which has huge economic implications in industrial processes. Poisoning can be selective: a substance may poison a metal catalyst for one reaction but not another.

催化剂中毒是指外来物质与催化剂的活性位点发生非常牢固（通常不可逆）的结合，阻止反应物分子与之接触。即使微量的毒物也能大幅降低催化活性，这在工业过程中具有重大的经济影响。中毒可以是选择性的：某种物质可能只毒化金属催化剂对某一反应的活性，而不影响其他反应。

Key examples from the CCEA syllabus: lead compounds poison platinum, palladium, and rhodium in catalytic converters, necessitating unleaded petrol; sulfur and arsenic impurities poison the iron catalyst in the Haber process, so natural gas feedstock must be desulfurised; and sulfur compounds poison nickel catalysts used in hydrogenation of alkenes to alkanes. Similarly, heavy metal ions such as Ag⁺ or Hg²⁺ can poison enzymes by binding to sulfur-containing cysteine residues.

CCEA 课程中的关键例子包括：铅化合物会毒化催化转化器中的铂、钯和铑，因此必须使用无铅汽油；硫和砷杂质会使哈柏法中的铁催化剂中毒，故天然气原料需预先脱硫；硫化合物会使烯烃加氢制烷烃的镍催化剂中毒。同样，Ag⁺ 或 Hg²⁺ 等重金属离子可与含硫的半胱氨酸残基结合而毒化酶。

Deactivation can also occur by physical means, such as sintering (loss of surface area due to crystal growth at high temperatures) or coking (deposition of carbonaceous residues that block pores). While physical deactivation is sometimes reversible by regeneration, chemical poisoning usually permanently ruins the catalyst. Understanding poisoning is essential for evaluating the lifetime, cost, and efficiency of an industrial catalyst.

失活也可由物理因素引起，例如烧结（高温下晶体长大导致表面积减小）或结焦（碳质残渣沉积堵塞孔道）。物理失活有时可通过再生逆转，但化学中毒通常会永久性毁坏催化剂。理解中毒对于评估工业催化剂的寿命、成本与效率至关重要。

11. The Role of Promoters and Supports | 促进剂与载体的作用

Promoters are substances that, while not catalysts themselves, enhance the activity or stability of a catalyst. In the Haber process, potassium oxide (K₂O) is added to the iron catalyst to promote the dissociation of N₂ by altering the electronic structure of the surface iron atoms; aluminium oxide (Al₂O₃) acts as a structural promoter, preventing the iron crystallites from sintering and

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Catalysis for CCEA A-Level Chemistry | A-Level CCEA 化学：催化 考点精讲