Catalyst and Catalysis催化剂与催化作用.doc

Catalyst and Catalysis催化剂与催化作用A catalyst increases the rate of a particular reaction without itself being used up. A catalyst can be added to a reaction and then be recovered and reused after the reaction occurs. 催化剂可以提高特定反应速率而自身却不会被消耗掉。催化剂可以被添加到反应中，在反应发生后可再回收再利用。The process or action by which a catalyst increases the reaction rate is called catalysis. The study of reaction rates and how they change when manipulated experimentally is called kinetics.催化剂可以提高反应速度, 这一过程称为催化作用。研究反应速率以及它们如何在实验中控制反应的速率被称之为动力学。Most chemical reaction occur as a series of steps. This series of steps is called a pathway or mechanism. Each individual step is called an elementary step. The slowest elementary step in a pathway determines the reaction rate. 大多数化学反应都是由一系列的反应步骤所构成。这一系列反应步骤称为反应途径或反应机理。每个单独的反应步骤称为一个基元反应步骤。最慢的一个基元反应步骤觉定了整个反应速率。 The reaction rate is the rate at which reactants disappear and products appear in a chemical reaction, or more specifically, the change in concentration of reactants and products in a certain amount of time.反应速率就是指在化学反应中反应物消耗和产物生成的速率，或更具体地说，是在一定的时间内反应物和产物的浓度的变化.While going through a reaction pathway, reactants enter a transitional state where they are no longer reactants, but are not yet products. During this transitional state they from what is called an activated complex.连续循环反应中，反应物首先生成过渡状态产物，这时它们不再是反应物，但也不是产物。过渡产物被称之为活化化合物。The activated complex is short-live and has partial bonding characteristics of both reactants and products. The energy required to reach this transitional state and form the activated complex in a reaction is called the activation energy.活化络合物是短暂存在的，同时具有反应物和产物的部分粘合特性。为了达到这一过渡的状态形成了复杂的反应活性所需的能量，称为活化能。In order for a reaction to occur, the activation energy must be reached. A catalyst increases the rate of reaction by lowering the activation energy required for the reaction to take place. The catalyst forms an activated complex with a lower energy than the complex formed without catalysis. 要使一个反应能够进行, 必须提供该反应所需的活化能。催化剂之所以能够增加反应速率,就是通过降低反应物所需要活化能.有催化剂参与的活性化合物比无催化参与的反应所需要的活化能量低。 This provides the reactants a new pathway which requires less energy. Although the catalyst lowers the activation energy required, it does not affect reaction equilibrium or thermodynamics. 催化剂提供了一个需要较少活化能的新反应途径。虽然催化剂降低了活化所需的能量，但它不会影响反应平衡和热力学。 The catalyst does not appear in the overall chemical equation for a pathway because the mechanism involves an elementary step in which the catalyst is consumed and another in which it is regenerated.催化剂不会出现在化学方程式中,因为整个反应过程中有些基元反应步骤消耗了催化剂,而另外一些基元反应步骤又再生了催化剂.Catalysts exist for all types of chemical reactions. A specific catalyst can be classified into one of two main groups: (i) Homogeneous; (ii) Heterogeneous. A catalyst that is in the same phase as the reactants and products involved in a reaction pathway is called a homogeneous catalyst. 催化剂存在于各种化学反应。可具体将催化剂分为之两大类：（一）均相;（二）多相。一种催化剂，在与反应物和反应途径涉及的产物具有相同的相称为均相催化剂。When a catalyst exists in a different phase than that of the reactants, it is called a heterogeneous catalyst. For example, nickel is a catalyst in the hydrogenation of vegetable oils.如果催化剂与反应物或者产物不是同一个相，那么这种催化剂被称为多相催化剂。例如，植物油氢化的催化剂Ni。Nickel is a solid, while the oil is a liquid, therefore nickel is a heterogeneous catalyst. An advantage of using heterogeneous catalysts is their ease of separation from the reactants and products involved in a pathway. 镍是固体，而石油是一种液体，因此镍是一种多相催化剂。使用多相催化剂的优点是能够方便地从反应物和生产物的中分离出来. Metals are often used as heterogeneous catalysts because many reactants adsorb to the metal surface, increasing the concentration of the reactants and therefore the rate of the reaction.金属通常被用来作为多相催化剂，因为许多反应物都容易吸附在金属表面，增加反应物浓度，因此，提高反应速率。Ionic interactions between metals and other molecules can be used to orient the reactants involved so that they react better with each other, or to stabilize charged reaction transition states. Metals also can increase the rate of oxidation-reduction (redox) reactions through changes in the metal ions oxidation state.金属离子和其他分子的离子相互作用可以影响反应物所涉及的反应方向，使他们更好地反应，或者能够使反应过程中的带电过渡态更加稳定。金属也能加快氧化还原反应是因为过渡金属是多价态.Another group of catalysts are called enzymes. Enzymes are proteins and therefore have a highly folded three-dimensional configuration. 另一组催化剂被称为酶。酶是蛋白质，因此具有高度折叠的三维立体构型.This configuration makes an enzyme particularly specific for a certain reaction or type of reaction. Enzymes tend to be more active, that is to say, they catalyze reactions faster than synthetic catalysts at ambient temperatures.这种三维立体构型使得酶在特丁的反应或者某一类反应中起到催化的作用。酶活性更高，也就是说，在常温下它们催化的反应的效率比合成催化剂还要好.There are endless reactions that can undergo catalysis. One example is the decomposition of hydrogen peroxide (H2O2).Without catalysis, hydrogen peroxide decomposes slowly over time to form water and oxygen gas. 有许多反应可以进行催化反应。其中一个例子就是过氧化氢分解。在没有催化的情况下，过氧化氢分解成水和氧气的速度非常慢。 A 30% solution of hydrogen peroxide at room temperature will decompose at a rate of 0.5% per year. The activation energy for this reaction is 75kJ/mol. This activation energy can be lowered to 58kJ/mol with the addition of iodide ions (I-).30%过氧化氢溶液在温室的条件下年分解率大约为0.5%。该反应的活化能为75KJ/mol.在有碘离子存在的条件下，活化能可以降低到58KJ/mol.These ions form an intermediate, HIO, which reacts with the hydrogen peroxide to regenerate the iodide ions. When the enzyme- catalase is added to the hydrogen peroxide solution, the activation energy is lowered even further to 4kJ/mol. 这些离子首先生成中间物质次碘酸, 而次碘酸又会与过氧化氢反应再生的碘。当酶（催化剂）被加入到过氧化氢溶液中时，活化能为进一步降低到4KJ/mol.The catalase is also regenerated in the reaction and can be separated from the solution for reuse. This example shows how a catalyst can lower the activation energy of a reaction without itself being used up in the reaction pathway. 双氧水分解酶催化剂可以在反应中重新生成还可以从溶液中分离出来再用。这个例子表明，催化剂在一个反应中可以降低活化能而本身又没有被消耗。Another example of catalysis is the catalytic converter of an automobile. Exhaust from the automobile can contain carbon monoxide and nitrogen oxides, which ate poisonous gases. 催化另一个例子是，汽车尾气催化转化器。汽车废气含有一氧化碳和氮氧化物等的有毒气体。Before the exhaust can leave the exhaust system these toxines must be removed. The catalytic converter mixes there gases with air and then passes them over a catalyst made of rhodium (Rh) and platinum (Pt) metals. 有害气体必须 在废气从排气管中排出前除去。尾气催化转化器将废气与空气混合，然后将它们通过由铑和铂金属制成的催化剂。This catalyst accelerates the reaction of carbon monoxide with oxygen and converts it to carbon dioxide, which is not toxic. The catalyst also increases the rate of reactions for which the nitrogen oxides are broken down into their elements.该催化剂加速了一氧化碳与氧气反应，将其转换为没有毒性的二氧化碳气体. 该催化剂同时也加速了对其中的氮氧化物分子分解为氧气和氮气的速度. A well-known example of catalysis is the destruction of the ozone layer. Ozone in the upper atmosphere serves as a shield for the harmful ultraviolet rays from the sun. 还有一个总所周知的例子就是催化反应对臭氧层的破坏，上层大气中的臭氧作为一个屏障来防止太阳紫外线的损害。Ozone(O3) is formed when an oxygen molecule(O2) is split into two oxygen atoms (O) by the radiation from the sun. The free oxygen atoms then attach to oxygen molecules to form ozone.臭氧的形成,是由氧分子在太阳辐射的情况下分裂成两个氧原子.游离的氧原子与氧分子结合从而形成臭氧.When another free oxygen atom reacts with the ozone molecule, two oxygen molecules ate formed. This is the natural destruction of ozone. 当另一个氧原子与臭氧分子发生反应，两个氧分子形成，这就是自然的破坏臭氧。Under normal circumstances, the rate of destruction of ozone is the same as the rate of ozone formation, so no net ozone depletion occurs. When chlorine atoms (Cl) are present in the atmosphere, they act as catalysts for the destruction of ozone.在正常情况下，臭氧破坏的速度跟臭氧形成的速率是相同的。因此没有出现净臭氧耗损.但是当大气层中出现了氯原子，它们充当了破坏臭氧的催化剂。Chlorine atoms in the atmosphere come from compounds containing chlorofluorocarbons (CFCs). CFCs are compounds containing chlorine, fluorine, and carbon. 大气中的氯原子来自于氟里昂的这种化合物。氟里昂化合物含有氯，氟和碳。 CFCs are very stable and can drift into the upper atmosphere without first being broken down. Once in the upper atmosphere, the energy from the sun causes the chlorine to be released.氟里昂非常稳定，可以进入高层大气而不先被分解。氟里昂一旦进入高层大气，太阳的辐射就能导致氯气被释放。The chlorine atom reacts with ozone to form chlorine monoxide (ClO) and an oxygen molecule. The chlorine monoxide then reacts with another oxygen atom to form an oxygen molecule and the regenerated chlorine atom. 氯原子和臭氧反应生成氧化氯和氧分子。随后的一氧化氯与另一个氧原子反应，生成氧气分子和再生氯原子。With the help of the chlorine catalyst, the degeneration of ozone occurs at a faster rate than its formation, which has caused a net depletion of ozone in the atmosphere.随着氯的催化作用下，臭氧层的衰退速度比它形成的速度更快.使之在大气层中形成臭氧层空洞.The former examples illustrate some of the many practical applications of catalysis. Almost all of the chemicals produced by the chemical industry are made using catalysis. 从上述的例证说明了许多催化反应的实际应用.几乎所有化工产品都采用催化反应来制取。Catalytic processes used in the chemical industry decrease production costs as well as create products with higher purity and less environmental hazards.在化工生产中使用催化剂不但降低生产成本,产品纯度更高而且对环境的危害更少。A wide variety of produces are made using catalytic processes. Catalysis is used in industrial chemistry, pharmaceutical chemistry, and agricultural chemistry, as well as in the specialty chemical industry. 各种各样的产品制取中都使用到催化剂。催化反应被广泛应用到工业化学，医药化工，农业化工还有某些特殊的化工行业。 Useful chemicals such as sulfuric acid