The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commer...The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commercial dealuminated Y zeolites(DAY)with different Si/Al ratios and meso/microporosities,with their properties analyzed by N_(2) adsorption/desorption,pyridine-IR,and hydroxyl-IR spectroscopy technologies.The global activity(conversion)is largely dependent on the concentration of the acid sites,and the activity of the protonic sites in terms of turnover frequency(TOF)reflects the accessibility of acid sites.The products of aromatics and isomers,and the yield of cracking products increase with the increase of concentration of strong protonic sites in zeolite micropores.Moreover,the decrease of aromatics with the reduction of the concentration of acid sites and the diffusion length within DAY zeolites are observed due to the decrease of the secondary reaction.For the same reason,it results in the increasing of C_(7)products and alkenes/alkanes ratios in the cracking products.The high i-C_(4)product selectivity is a unique reflection of the high percentage of very strong acid sites,which is characterized by the hydroxyl-IR band at 3600 cm^(-1).展开更多
随着超低排放要求的发布及工业生产过程的优化,高炉煤气的深度脱硫势在必行.本研究选用4个ZSM-5沸石分子筛,研究ZSM-5的表面酸性对其在模拟高炉煤气气氛中脱硫性能的影响.同时,采用XRD、SEM-ED5、^(29)Si MAS NMR、N_(2)吸/脱附和NH_(3)...随着超低排放要求的发布及工业生产过程的优化,高炉煤气的深度脱硫势在必行.本研究选用4个ZSM-5沸石分子筛,研究ZSM-5的表面酸性对其在模拟高炉煤气气氛中脱硫性能的影响.同时,采用XRD、SEM-ED5、^(29)Si MAS NMR、N_(2)吸/脱附和NH_(3)-TPD表征ZSM-5沸石分子筛的理化性质,并采用固定床装置评价其在模拟高炉煤气气氛中的H_(2)S脱除性能.结果表明,在模拟高炉煤气中,ZSM-5沸石分子筛具备较好的脱硫能力,随着硅铝比和钠铝比的升高,ZSM-5沸石分子筛的酸量和酸强度的降低,其H_(2)S穿透硫容也随之降低,H_(2)S的穿透硫容最高可达2.21 mg·g^(-1).进一步的研究表明,ZSM-5沸石分子筛的H_(2)S穿透硫容与中强酸和强酸的量有关,其中,强酸量的影响更大,其吸附H_(2)S的机理为羟基吸附机理.展开更多
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.21978192)the SINOPEC Technology Project(No.117009-1)the Shanxi Province Key Innovative Research Team in Science and Technology(No.2014131006).
文摘The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commercial dealuminated Y zeolites(DAY)with different Si/Al ratios and meso/microporosities,with their properties analyzed by N_(2) adsorption/desorption,pyridine-IR,and hydroxyl-IR spectroscopy technologies.The global activity(conversion)is largely dependent on the concentration of the acid sites,and the activity of the protonic sites in terms of turnover frequency(TOF)reflects the accessibility of acid sites.The products of aromatics and isomers,and the yield of cracking products increase with the increase of concentration of strong protonic sites in zeolite micropores.Moreover,the decrease of aromatics with the reduction of the concentration of acid sites and the diffusion length within DAY zeolites are observed due to the decrease of the secondary reaction.For the same reason,it results in the increasing of C_(7)products and alkenes/alkanes ratios in the cracking products.The high i-C_(4)product selectivity is a unique reflection of the high percentage of very strong acid sites,which is characterized by the hydroxyl-IR band at 3600 cm^(-1).
文摘目的综合评估心房颤动(房颤)导管消融围术期不间断新型口服抗凝剂(novel oral anticoagulants,NOACs)和华法林抗凝导致心脏压塞的风险。方法检索PubMed、EMBase和Cochrane Library数据库,获取从应用NOACs至2022年2月发表的房颤导管消融围术期NOACs不间断抗凝治疗和华法林不间断抗凝治疗导致心脏压塞的研究。并使用Cochrane偏倚风险评估工具和MINORS(methodological index for nonrandomized studies)进行文献质量评价,Review manager 5.3软件对所收集的数据进行统计学分析。结果共纳入13项研究,7701例房颤消融患者。此荟萃分析显示:房颤导管消融围术期不间断NOACs和华法林抗凝导致心脏压塞的风险差异无统计学意义(RR=0.79,95%CI:0.49~1.30,P=0.36)。亚组分析显示:房颤导管消融围术期NOACs和华法林不间断抗凝导致心脏压塞需要开胸手术干预或输血治疗的风险差异无统计学意义(RR=0.94,95%CI:0.48~1.86,P>0.05);不同种类的NOACs分别与华法林比较,均不增加心脏压塞的风险(P>0.05)。结论与不间断华法林抗凝相比,房颤导管消融围术期不间断NOACs抗凝并不增加心脏压塞的风险。
文摘随着超低排放要求的发布及工业生产过程的优化,高炉煤气的深度脱硫势在必行.本研究选用4个ZSM-5沸石分子筛,研究ZSM-5的表面酸性对其在模拟高炉煤气气氛中脱硫性能的影响.同时,采用XRD、SEM-ED5、^(29)Si MAS NMR、N_(2)吸/脱附和NH_(3)-TPD表征ZSM-5沸石分子筛的理化性质,并采用固定床装置评价其在模拟高炉煤气气氛中的H_(2)S脱除性能.结果表明,在模拟高炉煤气中,ZSM-5沸石分子筛具备较好的脱硫能力,随着硅铝比和钠铝比的升高,ZSM-5沸石分子筛的酸量和酸强度的降低,其H_(2)S穿透硫容也随之降低,H_(2)S的穿透硫容最高可达2.21 mg·g^(-1).进一步的研究表明,ZSM-5沸石分子筛的H_(2)S穿透硫容与中强酸和强酸的量有关,其中,强酸量的影响更大,其吸附H_(2)S的机理为羟基吸附机理.
