Hóa học của oxit lưu huỳnh trên bề mặt kim loại chuyển tiếp Kim loại chuyển tiếp các chất xúc tác không đồng nhất được sử dụng rộng rãi nhất trong ngành công nghiệp. Trong bài viết này, chúng ta sẽ tập trung sự chú ý của chúng tôi chủ yếu vào động cơ ô tô chất xúc tác khí thải đối với vấn đề môi trường. Để đáp ứng yêu cầu kiểm soát khí thải bằng ô tô tại Hoa Kỳ, vì vậy được gọi là chất xúc tác ba chiều, bao gồm Rh, Pt, Pd, đã được lựa chọn. | 4 Chemistry of Sulfur Oxides on Transition Metal Surfaces XI LIN and BERNHARDT L. TROUT Massachusetts Institute of Technology Cambridge Massachusetts . I. INTRODUCTION Transition metals are currently the most widely used heterogeneous catalysts in industry. In this article we shall focus our attention primarily on the automobile engine-out exhaust emission catalysts for environmental concerns. In order to meet automobile emission control requirements in the United States so-called three-way catalysts consisting of Rh Pt and Pd were selected to simultaneously convert CO hydrocarbons and NOx to CO2 H2O and N2 1 . In this conversion process both oxidation and reduction reactions take place on the same three-way catalyst surfaces. Therefore only a narrow range of air-to-fuel A F ratios around the stoichiometric point should be taken as the operating window of the catalytic conversion. However it is certainly desirable to have a wider A F range with a better rate of conversion of CO hydrocarbons and NOx. Lean-burning NOx-trapping catalysts were designed for this purpose. The idea is to separate the competing oxidation and reduction reactions by time via periodically alternating the A F ratio between lean high A F ratio and stoichiometric A F ratio conditions in the combustion chamber. Under lean conditions both CO and hydrocarbons can be efficiently oxidized to CO2 and H2O while NOx will be oxidized to the unfavorable chemical NO2. At the same time by introducing NOx-trapping materials such as BaO NO2 is trapped on the catalyst within this lean cycle. When the stoichiometric cycle is alternatively switched on the trapped NO2 is reversibly released from the BaO surface and further reduced to N2. However this novel lean-burn NOx-trap catalysis process has considerable practical problems due to serious sulfur poisoning issues described below . Before getting to the sulfur poisoning problem for the lean-burn NOx-trap catalyst let us examine how the traditional .
