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首页> 外文学位 >Oxidation catalysis in environmental applications: Nitric oxide and carbon monoxide oxidation for the reduction of combustion emissions and purification of hydrogen streams.
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Oxidation catalysis in environmental applications: Nitric oxide and carbon monoxide oxidation for the reduction of combustion emissions and purification of hydrogen streams.

机译：环境应用中的氧化催化：一氧化氮和一氧化碳氧化，用于减少燃烧排放和氢气流的净化。

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Cobalt based catalysts supported on TiO2 and ZrO 2 were studied for the oxidation of NO to NO2 in excess oxygen. NO oxidation was studied as the first step in a two-step catalytic scheme where NO is oxidized to NO2 and, in turn, NO2 is reduced with CH4 to N2 under lean conditions. Catalysts were prepared by sol-gel (SG) and incipient-wetness impregnation (IWI) techniques. It was found that increasing the calcination temperature had an adverse effect on the activity of the IWI catalysts. Catalysts were characterized by temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). 10%Co/ZrO2 IWI catalysts were found to be more active than the 10%Co/TiO2 IWI catalysts. The most active Co/ZrO2 catalyst reached equilibrium at 250°C, giving a 94% NO2 yield. Higher activity for NO oxidation was observed to correlate with the formation of the Co3O4 phase. Characterization by several techniques demonstrated that this metal oxide phase is more dominant on the ZrO2 support than on the TiO2 support.; For the second stage, reduction of NO2 with methane, a series of Pd-based catalysts on a sulfated zirconia (SZ) support were prepared and tested. The Pd/SZ catalysts showed much higher N2 yields during the reduction of NO2 as opposed to NO. When the Pd/SZ catalysts were combined with the cobalt-based NO oxidation catalysts for the reduction of NO with CH4 in excess O2, the N2 yields were similar to those obtained when only the reduction catalyst was used to reduce NO2. Studies in which the reactor feed contained species at concentrations that more closely resembled actual operating conditions (NOx, O2, CO, CO2, methane, ethane, and propane) showed promising results that did not significantly deviate from the N2 yields that were obtained in the earlier experiments. Experiments on the mixed catalyst bed in which water vapor was introduced to the feed led to a decrease in the N2 yield. The loss of activity in the presence of water has been attributed to competitive adsorption.; The studies for the reduction in NOx emissions also revealed that the cobalt-based NO oxidation catalysts had potential to be used as a catalyst for the oxidation of carbon monoxide. The Co/ZrO2 catalyst had high activity for the oxidation of CO to CO2, and under certain conditions was able to completely oxidize CO at room temperature. The catalyst was also studied for the preferential oxidation of carbon monoxide in excess hydrogen. While the oxidation of carbon monoxide in lean, excess oxygen, conditions has applications for air quality improvement, the preferential oxidation of carbon monoxide in the presence of hydrogen has application for the purification of hydrogen streams for use in PEM fuel cells. A range of test conditions with various gas-hourly space velocities and concentrations of CO, O 2, H2, CO2, and H2O were examined. It was found that an increase in the ratio of CO-to-O2 led to higher O2 selectivity to CO2 and lower conversion of CO for a given temperature. At a given temperature, the presence of CO2 or H2O led to an inhibition of the CO oxidation reaction and a decrease in the CO conversion, as compared to the reactions in which CO 2 or H2O were not present, was observed. The effect of GHSV showed that higher GHSV led to lower CO conversion but higher O2 selectivity to CO2. Stability studies showed that operation the catalyst in its oxide form was fairly stable while operating around 100°C, but operation at higher temperatures (175--250°C) could lead to a loss of activity, likely caused by the partial reduction of cobalt oxide. At higher temperatures, the reduction of cobalt oxide also led to the formation of methane through the CO + 2H2 methanation reaction. Cursory investigations of cobalt supported on various metal oxide supports showed that in the test conditions, Co/ZrO2 had the higher act
机译：研究了负载在TiO2和ZrO 2上的钴基催化剂在过量氧气中将NO氧化为NO2的能力。在两步催化方案中，第一步研究了NO氧化，其中NO被氧化为NO2，然后在稀薄条件下，NO2被CH4还原为N2。催化剂是通过溶胶-凝胶（SG）和初湿浸渍（IWI）技术制备的。发现提高煅烧温度对IWI催化剂的活性具有不利影响。催化剂的特征在于程序升温还原（TPR），X射线光电子能谱（XPS），X射线衍射（XRD），激光拉曼光谱（LRS）和漫反射傅里叶变换红外光谱（DRIFTS）。发现10％Co / ZrO2 IWI催化剂比10％Co / TiO2 IWI催化剂更具活性。活性最高的Co / ZrO2催化剂在250°C达到平衡，NO2收率达到94％。观察到较高的NO氧化活性与Co3O4相的形成有关。用几种技术表征表明，该金属氧化物相在ZrO2载体上比在TiO2载体上更占优势。对于第二步，用甲烷还原NO2，制备并测试了一系列在硫酸化氧化锆（SZ）载体上的Pd基催化剂。与NO相比，Pd / SZ催化剂在NO2还原过程中显示出更高的N2收率。当将Pd / SZ催化剂与钴基NO氧化催化剂混合以用过量O2中的CH4还原NO时，N2收率类似于仅使用还原催化剂还原NO2时获得的收率。研究表明，反应器进料中所含物质的浓度与实际操作条件（NOx，O2，CO，CO2，甲烷，乙烷和丙烷）更接近，显示出令人鼓舞的结果，该结果并未显着偏离较早的实验。在其中将水蒸气引入进料中的混合催化剂床上的实验导致N 2收率降低。在水存在下活性的丧失归因于竞争性吸附。减少NOx排放的研究还表明，钴基NO氧化催化剂有潜力用作一氧化碳氧化的催化剂。 Co / ZrO2催化剂具有将CO氧化为CO2的高活性，并且在一定条件下能够在室温下完全氧化CO。还研究了该催化剂用于过量氢气中一氧化碳的优先氧化。尽管在贫氧，过量氧气条件下氧化一氧化碳可改善空气质量，但在氢气存在下优先氧化一氧化碳可用于纯化用于PEM燃料电池的氢气流。检验了具有各种气体时空速度和CO，O 2，H2，CO2和H2O浓度的一系列测试条件。发现在给定温度下，CO与O 2的比率的增加导致较高的O 2对CO 2的选择性和较低的CO转化率。与不存在CO 2或H 2 O的反应相比，在给定的温度下，CO 2或H 2 O的存在导致CO氧化反应的抑制和CO转化率的降低。 GHSV的作用表明，较高的GHSV导致较低的CO转化率，但O2对CO2的选择性更高。稳定性研究表明，以氧化物形式运行的催化剂在100°C左右运行时相当稳定，但在较高温度（175--250°C）下运行可能导致活性下降，这可能是由于钴的部分还原所致氧化物。在较高的温度下，氧化钴的还原还导致通过CO + 2H2甲烷化反应生成甲烷。对各种金属氧化物载体上的钴进行的课程研究表明，在测试条件下，Co / ZrO2具有较高的作用

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