催化与化学催化剂

发布时间：2016-05-11 16:09

Introduction介绍

催化剂加快数量级，从而使他们能够在最有利的热力学系统，并且在较低的温度和压力下反应。在这种方式的反应器和设备的设计和高效率的催化剂的组合的优化用于降低投资和操作成本是在化学过程中的关键要素。
本报告旨在批判性地分析催化的概念，并用碰撞理论来解释催化剂的反应。此外，它是如何均相和非均相催化剂的工作区分。最后，结论是基于前面的分析得出。
Catalysts speed up by orders of magnitude, so that they can in the most favorable thermodynamic systems and reaction at lower temperatures and pressures. In this way reactor and plant design and optimization of combination of high efficiency catalyst for reducing investment and operating costs are key elements in a chemical process.
This report aims to critically analyse the concept of catalysis and use collision theory to explain the reaction of catalyst. Moreover, it distinguish between how homogeneous and heterogeneous catalysts work. Finally, a conclusion is drawn based on previous analysis. 

Define catalysis定义催化

催化剂提供了低活化能的反应不同的途径。反应速度快，因为更多的分子具有最低活化能。催化剂被消耗，并且响应出现在生产整体式的。的压力和温度条件下的催化剂提供替代方案中，能量上有利的以非催化反应机制，使得加工工业上可行的。催化剂加速化学反应。它是通过反应和分子键形成，并允许这些对产品，其中在催化剂的作用分离，让它是相同的，它可用于下一个响应来响应。实际上，催化反应可以被描述为一个循环，其中事件的催化剂参与，并且在循环结束在其原来的形式恢复。反应催化剂是由它的增加的应答的化合物的加快而本身被消耗的反应或的（循环）的变化的结束。这指的是催化反应。在加速响应催化剂称为催化方法。A catalyst provides a different pathway for the reaction of lower activation energy. Reaction speed, because more molecules have minimum activation energy. Catalyst is consumed, and responses appear in the production of the overall equation. A catalyst provide alternative, energetically favorable to non-catalytic reaction mechanism, making processed industrially viable under conditions of pressure and temperature. Catalysts speed up chemical reactions. It is formed by reaction and molecular bonds and allow these to a product, which separated in the catalyst role, let it be the same, it can be used to respond to the next response. In fact, the catalytic reaction can be described as a loop in which the catalyst of events to participate in, and restored in its original form at the end of the cycle. Reaction catalyst is a compound by its increased response speeds up the reaction without itself being consumed or the end of the (cycle) changes. This refers to catalytic reaction. Catalyst in accelerating response is called a catalytic process.

Collision theory 碰撞理论

Collision theory is used to explain the General conditions that must be satisfied the established theory of chemical reactions. Collision theory point out that the following three conditions must be applied in order for a successful product of a chemical reaction formed in line with. 1. It must have sufficient frequency of collisions between the reactants. 2. The reactants must work with the appropriate orientation or collision geometry, such that the reactive power together. 3. the energy of the reactants must be equal to or greater activation energy. The activation energy (Ea) in order for reactants collide with enough energy in the reactants to break the bonds that can form the required minimum energy (e ≥ Ea).
 
Figure 1.1 
Use enthalpy profiles of reaction to explain how catalysis work
It had always been the catalytic reaction two molecules a and b, p, as shown in Figure 1.2. Cycle starts with a combination of molecular catalysts for a and b. Within this complex and then respond to a and b, p, is bound to act as a catalyst. In the final step, p from catalyst separation and thus out of the reaction cycle in its original state.
 
Figure 1.2 Every reaction is catalyzed by a series of fundamental steps which reactant molecules will bind to the catalytic role, their reaction after separation of catalyst, emancipation, the latter for the next cycle. 
Catalysts speed up how you want to view, and look at potential energy diagram, catalytic and non-catalytic reactions are compared. For non-catalytic reactions, the illustration is simple and familiar way to visualize the alunniwusi equation: the reaction proceeds of a and b collide with enough energy to overcome the activation barrier. Gibbs free energy of reaction, a + b, and p is the product of change between DG. Catalysts for catalytic reactants, a and b, in a spontaneous reaction of bonding begins. Therefore, the formation of this complex is a fever, and the free energy is lowered. Then the reaction between a and b, which is bound to the catalyst. This step is the activation energy; associate, however, it is significantly lower than non-catalytic reactions. Finally, a step towards the separation of product p from catalysts for endothermic.

Distinguish between how homogeneous and heterogeneous catalysts work
Homogeneous Catalysis
Homogeneous catalytic reactions, catalysts and reactants at the same stage that all molecules in the gas phase, or, more common is that in the liquid phase. A most simple example is found in atmospheric chemistry. Decomposition of ozone in the atmosphere, and on other routes, by reaction with chlorine atoms

Cl + O3    ClO3
ClO3    ClO + O2
ClO + O    Cl + O2
or overall
O3 + O →2O2
It can be spontaneous and light, but Cl atoms accelerated reactions under the influence is enormous. When it left unchanged the reaction cycle, Cl atom is a catalyst. Since both reactants and catalyst during the same period, the gas-phase reaction cycle is an example of phase. (This is the ozone hole was historically important in the prediction. Industries use large amounts of homogeneous catalysts in the reactions of all kinds of production chemicals. Catalytic synthesis of acetic acid by methanol carbonylation for CH3OH + CO → ch3cooh) by [Rh (CO) 2I2]--complexes in solution is one of many examples. Homogeneous catalytic reactions tend to produce subtle pharmaceutical,organometallic complexes employed during synthesis of molecular control, smart choice indicates that the reaction of the ligand molecules to a desired product.
Heterogeneous Catalysis
In heterogeneous catalytic reactions catalyzed by solid gas or liquid molecules. As solid-unless they are porous--is airtight, catalytic reaction takes place on the surface. To use in the economy, usually expensive material (such as Platinum), catalysts are typically nano particles in support of inert and porous structure. Example: critical responses in the cleaned automotive exhaust catalytic CO oxidation on the surface of precious metals such as Platinum, palladium and rhodium. Catalytic reaction cycle beginning of Platinum, by to O2 molecular dissociation into two a o Atomic surface adsorption of CO and O2 (x * indicates of atomic or molecular adsorption in surface, that bound to the site *): O2 _ 2_ _ 2O_CO__ _ min-was adsorption of o Atomic and adsorption of CO molecular then to surface Shang made reaction formed CO2, which is very stable and relative inert, only weak to interactive and in Platinum surface and desorbs almost in moments completed: min-_ O__CO2 _ 2_ Please note that in the latter step adsorption sites on the catalyst free, and so these become available for further reaction cycles. Cycle of reaction and a potential energy diagram.

Conclusion总结

Catalysts speed up so that the industrially important reactions, under actual conditions can be achieved effectively. In many cases, the efficient use of materials and waste minimization, design of catalytic route. Therefore, the chemical industry is to a large extent based on catalytic: along the 85-90% of all products in the catalytic process, and the percentage has increased steadily.

References文献

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Green, J. and Sadru, D. (2007) Chemistry for use with the International Baccalaureate Programme. Melbourne: IBID Press.

Neuss, G. (2007). IB Diploma Programme Chemistry Course Companion. Oxford: Oxford University Press.

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