DEVELOPMENT OF GAS SENSORS AND DECOMPOSITION CATALYST SYSTEM FOR NITROUS OXIDE USED IN OPERATING ROOMS

一氧化二氮（N_2O）是一种广泛用于外科手术的麻醉气体，其产生的N_2O废气不经处理即释放到大气中。由于N_2O是一种温室效应气体，其全球变暖系数比CO_2高300倍左右，同时也是破坏臭氧层的重要气体之一，因此N_2O的释放对大气环境有着重要的危害。因此，在释放N_2O之前，最好将N_2O催化分解为N_2和O_2。近年来有报道指出，N_2O对室内空气的污染可能对在这种条件下工作的人员造成健康危害。N_2O传感器为了研制适用于空气中N_2O监测的半导体型气体传感器，对N_2O敏感的半导体氧化物进行了研究。在所测试的23种单一氧化物中，SnO_2最好 ...更多信息 对N_2O的灵敏度最高，但灵敏度不够高。在SnO_2中加入少量的碱性氧化物SrO、CaO、BaO、Bi_2O_3和Sm_2O_3，可有效地提高SnO_2的N_2O灵敏度。这种促进作用在SrO负载下尤为明显。以SnO_2为例，研究了以稳定氧化锆为基体，氧化物为电极的电化学装置对空气中N_2O的检测性能。结果表明，当SnO_2中SrO含量为0. 5wt%时，N_2O的灵敏度是纯SnO_2的3倍，在10-300 ppm的浓度范围内，N_2O的检测效果良好。在所测试的11种一氧化物中，SnO_2具有最好的敏感电极性能，在475 ℃空气中具有较高的灵敏度。添加外来氧化物（例如，Bi_2O_3和Sm_2O_3对SnO_2的改性能有效提高N_20的灵敏度。其中Sm_2O_3（0.5wt%）-SnO_2敏感电极的灵敏度是纯SnO_2敏感电极的1.5倍，可检测空气中约35 ppm的N_2O。2）N_2O分解催化剂对40多种催化剂进行了筛选试验，它们是负载在氧化物载体如沸石、Al_2O_3、TiO_2或SiO_2上的过渡金属或贵金属催化剂。所有的催化剂都能直接分解N_2O，但催化剂的活性对活性组分和载体有很大的依赖性。在这些催化剂中，负载金属的Al_2O_3表现出最强的分解活性，实际水平取决于活性组分（Pd>Ru>Pt）。在活性最高的催化剂（5wt%Pd/Al_2O_3）中，N_20的直接分解反应在250℃左右开始，在300℃左右完全。5wt%Pd/Al_2O_3催化剂的N_2O分解活性受共存水的抑制，但在2.3%的水存在下仍保持较高的活性，300℃和400℃时N_2O分解开始并完全，3）.手术室N_2O的现场监测结果表明，手术室内N_2O浓度达100 - 200 mg/L，手术室内N_2O浓度为100 - 200 mg/L，手术室内N_2O浓度为100- 200 mg/L，手术室内N_2O浓度为100- 200 mg/L，手术室内N_2O浓度为100- 200 mg/L。150 ppm时，清除系统没有工作良好。尤其是患者和/或麻醉气体供应设备附近的N_2O浓度大于500 ppm。少

Nitrous oxide (N_2O), called "laughing gas", is an anesthetic gas used extensively for surgical operations where waste N_2O is released into the atmosphere without treatment. This release may be hazardous to the atmospheric environment, since N_2O is a green-house-effect gas, the global warming coefficient of which is about 300 times higher than that of CO_2, beside being one of the gases leading to ozone layer disruption. It is thus desirable to catalytically decompose N_2O into N_2 and O_2 before release. It has recently been reported that contamination of indoor atmospheres with N_2O may cause health hazards for staff routinely working under such conditions. This project aims to develop a catalytic N_2O decomposition system and N_2O sensor.1).N_2O sensorsIn order to develop a semiconductor type gas sensor applicable to the monitoring of N_2O in air, a search for the semiconducting oxides sensitive to N_2O was carried out. Among the 23 kinds of single oxides tested, SnO_2 turned out … More to give the highest sensitivity to N_2O, although the sensitivity was not high enough. The N_2O sensitivity was found to be promoted effectively when SnO_2 was loaded with a small amount of a basic oxide such as SrO, CaO, BaO, Bi_2O_3 and Sm_2O_3. The promotion was particularly conspicuous with SrO loading. For example, 0.5wt%SrO-loaded SnO_2, exhibited the N_2O sensitivity about 3 times as high as that of pure SnO_2, and could detect N_2O in air fairly well in the concentration range of 10-300 ppm.A stabilized-zirconia based electrochemical device attached with an oxide electrode was developed for monitoring N_2O in air at elevated temperatures. Among the 11 kinds of monoxides tested for tubular zirconia device, SnO_2 was found to exhibit the best sensing electrode properties, giving a relatively high sensitivity in air at 475 ℃. The addition of a foreign oxide (e.g., Bi_2O_3 and Sm_2O_3 to SnO_2 was effective to improve the N_20 sensitivity. Especially the element using Sm_2O_3 (0.5wt%)-SnO_2 sensing electrode exhibited the N_2O sensitivity about 1.5 times as high as that using the pure SnO_2 electrode, allowing to detect about 35 ppm N_2O in air. On the basis of the measurements of anodic and cathodic polarization curves, the sensing mechanism was confirmed to involve a mixed potential at the sensing electrode.2).N_2O decomposition catalystsMore than 40 catalysts were subjected to the screening test ; they were transition or precious metal catalysts loaded onto oxide supports such as zeolites, Al_2O_3, TiO_2, or SiO_2. The direct decomposition of N_2O proceeded with all the catalysts tested, but the activity was strongly dependent on both the active ingredient and the support. Among these catalysts, metal-loaded Al_2O_3 exhibited the most potent decomposition activity, the actual level depending on the active ingredient (Pd>Ru>Pt). With the most active catalyst (5wt% Pd/Al_2O_3), the direct decomposition of N_20 from the dry model gas started around 250℃ and reached completion at 300℃. Although the decomposition activity was inhibited by co-existing water, 5wt%Pd/Al_2O_3 retained its high activity even in the presence of 2.3% water, N_2O decomposition starting and being completed at 300℃ and 400℃, respectively.3).Field monitoring of N_2O at a operating roomIt was found that the ambient N_2O concentration in an operating room reached 100-150ppm when a scavenging system did not work well. Especially, the N_2O concentration near a patient and/or equipment for anesthetic gas supply was more than 500 ppm. Less