浸渍顺序对Zn改性Cr/SiO_2催化剂在CO_2氧化乙烷脱氢制乙烯反应中催化性能的影响

通过改变浸渍顺序分别制备了Cr(10)-Zn(5)/SiO_2、Zn(5)/Cr(10)/SiO_2和Cr(10)/Zn(5)/SiO_2催化剂,并在微型石英反应器中对这三种催化剂的催化性能进行了研究。结合XRD、TG、TPR和TPD-CO_2表征技术,研究了浸渍顺序对催化剂结构性能的影响。实验结果表明,Cr(10)/Zn(5)/SiO_2和Cr(10)-Zn(5)/SiO_2催化剂上ZnCr_2O_4物种的晶粒尺寸比较小,从而表现出较高的初始催化活性,乙烷转化率分别为58. 8%和53. 4%。经过10 h的反应,在Cr(10)/Zn(5)/SiO_2和Cr(10)-Zn(5)/SiO_2催化剂上检测到较多的积碳,从而使催化剂失活。Zn(5)/Cr(10)/SiO_2催化剂上存在大量的Cr~(6+)物种,同时检测到较大晶粒尺寸的ZnCr_2O_4物种,初始催化活性比较低,乙烷转化率仅为48. 2%。但是经过10 h的反应,Zn(5)/Cr(10)/SiO_2催化剂表现出较好的稳定性。     

Camera calibration approach using circle-square-combined target

Calibrating a small field camera is a challenging task because the traditional target with visible feature points that fit the limited space is difficult and costly to manufacture.We demonstrate a novel combined target used in camera calibration.The tangent points supplied by one circle located at the center of a square are used as invisible features,and the perspective projection invariance is proved.Both visible and invisible features extracted by the proposed feature extraction algorithm are used to solve the calibration. The target supplies a sufficient number of feature points to satisfy the requirements of calibration within a limited space.Experiments show that the approach can achieve high robustness and considerable accuracy. This approach has potential for computer vision applications particularly in small fields of view.