CN117065760A - 一种尖晶石@CeO2催化剂及其制备方法和应用 - Google Patents
一种尖晶石@CeO2催化剂及其制备方法和应用 Download PDFInfo
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Abstract
本发明涉及大气污染催化剂制备技术领域,具体是涉及一种尖晶石@CeO2催化剂及其制备方法和应用;其中制备方法为:S1、合成具有氧化性金属的MOFs;S2、氧化还原锚定合成尖晶石@CeO2;S3、限域热解制备尖晶石@CeO2异质结催化剂;本发明利用MOFs的氧化性、结构多样性、金属簇高度分散性驱动其与具有还原性的Ce(OH)3发生氧化还原反应,实现了CeO2均匀锚定在MOFs中高度有序的具有氧化性金属簇中,进而实现了通过调节尖晶石@CeO2异质结催化剂中两组分间相互作用以及异质结界面来提高催化剂的本征活性的催化剂改性策略,从而制备出具有良好低温活性的VOCs催化氧化用催化剂。
Description
技术领域
本发明涉及大气污染催化剂制备技术领域,具体是涉及一种尖晶石@CeO2催化剂及其制备方法和应用。
背景技术
有效治理VOCs对提高大气污染防治具有重要意义,在众多VOCs处理方法中,催化氧化法具有众多优势,因此其高效催化剂的研制具有实际意义。对于上述问题,CeO2因其具有良好的氧储存能力受到了本领域的技术人员的青睐,基于CeO2研制出了多种复合催化剂,如:
《CeO2 from pyrolysis of MOFs for efficient catalytic combustion ofVOCs》(DOI:10.1016/J.MCAT.2022.112857)一文公开了通过热解UiO-66(Ce)制备具有MOF结构CeO2催化剂,通过催化剂的微孔结构提高对VOCs的催化性能。
《Catalytic Ozonation of Norfloxacin Using Co-Mn/CeO2 as aMulti-Component Composite Catalyst》一文公开了通过在CeO2上负载Co、Mn组元,以增加催化剂表面活性位点的方式提高催化剂的催化性能。
不同与上述以CeO2作为骨架负载过渡金属或改善CeO2本身机构的方法,本发明以全新的合成路径制备了尖晶石@CeO2催化剂,该催化剂因存在CeO2与尖晶石间的异质结结构,因而能够提高催化本征活性,且本发明通过新的合成路径解决了现有方法中存在的下述共性难题:
1)由于尖晶石和CeO2两组分物化性质差距大,使得CeO2难以分散在尖晶石表面,不利于活性异质结界面的形成;
2)传统方法如氧化还原法构筑的尖晶石@CeO2异质结催化剂比表面积小,不利于活性异质结界面的形成;
3)传统方法如模板法构筑的尖晶石@CeO2异质结催化剂,CeO2与尖晶石相互作用弱,不利界面电子传送导致对催化剂本征活性提高有限。
发明内容
为了实现以上目的,本发明利用MOFs与具有还原性的Ce(OH)3发生氧化还原反应,实现了CeO2均匀锚定在MOFs中高度有序的具有氧化性金属簇中,进而实现了通过调节尖晶石@CeO2异质结催化剂中两组分间相互作用以及异质结界面来提高催化剂的本征活性的催化剂改性策略,最终制备出具有良好低温活性的VOCs催化氧化用催化剂,技术方案如下:
1、尖晶石@CeO2催化剂,
本发明设计的尖晶石@CeO2催化剂包括尖晶石和通过界面反应锚定在尖晶石表面上的CeO2颗粒,具有下述结构特征:
尖晶石为具有氧化性金属的MOFs通过限域热解得到;
界面反应锚定CeO2过程是通过具有氧化性金属的MOFs与碱性条件下Ce3+发生氧化还原反应实现的;
氧化性金属为金属氰化物;
MOFs包括立方状的尖晶石和均匀分布在尖晶石上作为氧化位点的金属氰化物;
尖晶石@CeO2催化剂具有异质结结构,比表面积为133-296g/m2,其中二氧化铈的粒径大小为2.1~16.2nm。
2、一种尖晶石@CeO2催化剂的制备方法
本发明设计的一种尖晶石@CeO2催化剂的制备方法,步骤包括:
S1、通过共沉淀法合成具有氧化性金属的MOFs;
S2、保护氛围、微波加热下,通过氧化还原反应于S1得到的具有氧化性金属的MOFs的表面锚定CeO2颗粒,得到MOFs@CeO2;
S3、热解S2中MOFs@CeO2,生成具有异质结结构的尖晶石@CeO2催化剂;
S1中,共沉淀法中使用的溶液包括溶液A和溶液B:
溶液A为:含过渡金属盐的水溶液,或含过渡金属盐和表面活性剂的水溶液;溶液B为:含金属氰化物的水溶液;
溶液A和溶液B的混合方法为:搅拌下,将溶液B逐滴加入溶液A,并持续搅拌0.2~3h;
共沉淀法老化参数为:室温下老化5~24h;
说明:金属氰化物中金属离子为+3具有氧化性,其与过渡金属盐形成MOFs也继承了金属氰化物的氧化性,进而能驱动具有还原性物质发生氧化还原反应;同时MOFs中金属簇具有高度有序特性,为其在MOFs空间原子级锚定创造条件;
S2中,氧化还原反应中的还原物为:
由Ce(NO3)3·6H2O与NH3释放剂反应生成的Ce(OH)3;
微波加热的参数为:微波功率为400W~500W,反应温度为60℃~70℃,反应时间为2h~3h;
说明:氮气保护下,排除了制备过程中氧气的干扰;S2中NH3释放剂受热产生NH3与Ce3+结合形成具有强还原性的Ce(OH)3,进而能与MOFs中高度有序的具有氧化性金属簇发生氧化还原反应,使CeO2均匀锚定在MOFs中高度有序的具有氧化性金属簇中,提高了CeO2与MOFs间相互作用还实现CeO2原子级分散,有利于其衍生的尖晶石@CeO2异质结催化剂中CeO2与尖晶石异质结界面电子传送,提高催化剂本征活性;同时MOFs结构多样性既有利于CeO2与尖晶石异质结界面的形成,还有利于VOCs、O2、氧化产物在催化剂表面扩散;此外,MOFs发生还原反应,为保持电中性产生大量缺陷,进而有利于热解过程形成氧空位,氧空位是VOCs催化氧化过程活性位点,能提高催化剂的低温活性。
S3中,热解的参数为:空气气氛下,以1℃/min~2℃/min的升温速率升温至300℃~400℃,持续焙烧3-4h;
说明:表面锚定的二氧化铈能形成限域效应,有利于热解过程MOFs结构不坍塌,使尖晶石@CeO2异质结催化剂继承MOFs形貌和孔结构。
进一步地,制备方法包含的反应体系为体系A或体系B中的一个:
体系A中:
S1中:过渡金属盐为MnCl2·4H2O,金属氰化物为K3Co(CN)6;
S2中:NH3释放剂为六亚甲基四胺;
体系B中:
S1中:过渡金属盐为Ni(NO3)2·6H2O,表面活性剂为聚吡咯烷酮,金属氰化物为Na3Co(CN)6;
S2中:NH3释放剂为氯化铵。
进一步地,体系A中:
S1中:过度金属盐与金属氰化物的摩尔比为10:28;
S2中:MOFs、Ce(NO3)3·6H2O和NH3释放剂的质量比为8:(2~3):4;
体系B中:
S1中:所述过渡金属盐、表面活性剂和金属氰化物的摩尔比为40:1:30;
S2中:MOFs、Ce(NO3)3·6H2O和NH3释放剂的质量比为10:2:7。
与现有的用于分解VOCs的CeO2基催化剂相比,本发明的有益效果是:
(1)本发明巧妙利用MOFs的氧化性、结构多样性、金属簇高度分散性驱动其与具有还原性的Ce(OH)3发生氧化还原反应,实现了CeO2均匀锚定在MOFs中高度有序的具有氧化性金属簇中中,提高了CeO2与MOFs间相互作用还实现CeO2原子级分散,有利于其衍生的尖晶石@CeO2异质结催化剂中CeO2与尖晶石异质结界面电子传送,提高催化剂本征活性;同时MOFs结构多样性既有利于CeO2与尖晶石异质结界面的形成,还有利于VOCs、O2、氧化产物在催化剂表面扩散。此外,MOFs发生还原反应,为保持电中性产生大量缺陷,进而有利于热解过程形成氧空位,氧空位是VOCs催化氧化过程活性位点,能提高催化剂的低温活性。
(2)本发明CeO2锚定在MOFs表面能形成限域效应,表面锚定的二氧化铈能形成限域效应,有利于热解过程MOFs结构不坍塌,使尖晶石@CeO2异质结催化剂继承MOFs形貌和孔结构,解决MOFs材料热解过程中结构易坍塌的难题。
(3)本发明制备的尖晶石@CeO2异质结催化剂具有优良的低温活性:以甲苯转化率为90%的对应温度T90%作为催化剂活性评价标准,在甲苯初始浓度为1000ppm以及5%vol水蒸气条件下,0.1g尖晶石MOFs@CeO2催化剂的T90%为228℃,较之常规催化剂能耗大大降低。
附图说明
图1是本发明中CoMn-MOFs、CoMn-MOFs@CeO2和CoMn@CeO2-0.2的XRD图;
图2中:
(a)为CoMn-MOFs的SEM图;
(b)为CoMn@CeO2-0.2的SEM图;
(c)为CoMn@CeO2-0.2的HRTEM图;
(d)为CoMn@CeO2-0.2中Mn、Co、Ce、O的Mapping图。
具体实施方式
为更进一步阐述本发明所采取的方式和取得的效果,下面将结合附图对本发明的技术方案进行清楚和完整地描述。
实施例1
实施例1依以下步骤制备尖晶石@CeO2异质结催化剂CoMn@CeO2-0.2。
(1)合成具有氧化性金属的CoMn-MOFs:将5.95g MnCl2·4H2O溶解于100mL水中形成溶液A,待用;将3.1g K3Co(CN)6溶解于100mL水中形成溶液B,随后,在磁力搅拌下,将溶液B逐滴加入溶液A,继续搅拌0.5h,随后停止搅拌,在室温下老化5h,将反应后产物用乙醇或水清洗、干燥后即可得具有氧化性金属的CoMn-MOFs。
(2)氧化还原锚定合成CoMn-MOFs@CeO2:将0.8g(1)中具有氧化性金属的CoMn-MOFs和0.2g Ce(NO3)3·6H2O超声分在160mL水和160mL乙醇混合溶液中,随后将0.4g六亚甲基四胺充分溶解于上述溶液中,随后,在氮气保护下将上述溶液中放入微波反应器中在400W加热功率下于70℃反应2h,将反应后产物用乙醇或水清洗、干燥后即可得CoMn-MOFs@CeO2。
(3)限域热解制备尖晶石@CeO2异质结催化剂:将(2)中MOFs@CeO2放入管式炉中,然后在空气的气氛下以2℃/min的升温速率升至400℃焙烧3h即可得到尖晶石@CeO2异质结催化剂CoMn@CeO2-0.2。
由图1可知,CoMn-MOFs、CoMn-MOFs@CeO2和CoMn@CeO2-0.2的XRD图与标准卡片匹配,说明成功制备了相应的产物。由图2(a)和(b)可知,CoMn@CeO2-0.2和CoMn-MOFs都呈三维立方状,表明CoMn@CeO2-0.2合成过程CoMn-MOFs起到了模板作用,三维立方状既有利于CoMn尖晶石与CeO2异质结界面的形成,还有利于VOCs、O2、氧化产物在催化剂表面扩散。由图2(c)可发明CeO2与CoMn尖晶石间形成了异质结结构。由图2(d)可知,CoMn@CeO2-0.2中Mn、Co、Ce、O均匀分布。以上结果表明本发明的方法可以成功制备尖晶石@CeO2异质结催化剂,且CeO2均匀分布在尖晶石表面,同时还以通过调节MOFs形貌和结构来实现催化剂调控异质结界面有效调控。
实施例2
实施例2依以下步骤制备尖晶石@CeO2异质结催化剂CoMn@CeO2-0.3。
(1)合成具有氧化性金属的CoMn-MOFs:将5.95g MnCl2·4H2O溶解于100mL水中形成溶液A,待用;将3.1g K3Co(CN)6溶解于100mL水中形成溶液B,随后,在磁力搅拌下,将溶液B逐滴加入溶液A,继续搅拌0.5h,随后停止搅拌,在室温下老化5h,将反应后产物用乙醇或水清洗、干燥后即可得具有氧化性金属的CoMn-MOFs。
(2)氧化还原锚定合成CoMn-MOFs@CeO2:将0.8g(1)中具有氧化性金属的CoMn-MOFs和0.3g Ce(NO3)3·6H2O超声分在160mL水和160mL乙醇混合溶液中,随后将0.4g六亚甲基四胺充分溶解于上述溶液中,随后,在氮气保护下将上述溶液中放入微波反应器中在400W加热功率下于70℃反应2h,将反应后产物用乙醇或水清洗、干燥后即可得CoMn-MOFs@CeO2。
(3)限域热解制备尖晶石@CeO2异质结催化剂:将(2)中MOFs@CeO2放入管式炉中,然后在空气的气氛下以2℃/min的升温速率升至400℃焙烧3h即可得到尖晶石@CeO2异质结催化剂CoMn@CeO2-0.3。
实施例3
实施例3依以下步骤制备尖晶石@CeO2异质结催化剂CoNi@CeO2-0.2。
(1)合成具有氧化性金属的CoNi-MOF:将00.632g Ni(NO3)2·6H2O和0.7g聚吡咯烷酮溶解于100mL水中形成溶液A,待用;将0.446gNa3(Co(CN)6)溶解于100mL水中形成溶液B,随后,在磁力搅拌下,将溶液B逐滴加入溶液A,继续搅拌1h,随后停止搅拌,在室温下老化24h,将反应后产物用乙醇或水清洗、干燥后即可得具有氧化性金属的CoNi-MOFs。
(2)氧化还原锚定合成CoNi-MOFs@CeO2:将1g(1)中具有氧化性金属的CoNi-MOFs和0.2g Ce(NO3)3·6H2O超声分在160mL水和160mL乙醇混合溶液中,随后将0.7g氯化铵充分溶解于上述溶液中,随后,在氮气保护下将上述溶液中放入微波反应器中在500W加热功率下于60℃反应3h,将反应后产物用乙醇或水清洗、干燥后即可得CoNi-MOFs@CeO2。
(3)限域热解制备尖晶石@CeO2异质结催化剂:将(2)中MOFs@CeO2放入管式炉中,然后在空气的气氛下以1℃/min的升温速率升至300℃焙烧4h即可得到尖晶石@CeO2异质结催化剂CoNi@CeO2-0.2。
对比例1
对比例1合成CoMn尖晶石催化剂:与实施列1合成方法相同,不同之处在于合成过程没有添加Ce(NO3)3·6H2O,具体步骤如下:
(1)合成具有氧化性金属的CoMn-MOFs:将5.95g MnCl2·4H2O溶解于100mL水中形成溶液A,待用;将3.1g K3Co(CN)6溶解于100mL水中形成溶液B,随后在磁力搅拌下,将溶液B逐滴加入溶液A,继续搅拌0.5h,随后停止搅拌,在室温下老化5h,将反应后产物用乙醇或水清洗、干燥后即可得具有氧化性金属的CoMn-MOFs。
(2)合成CoMn-MOFs-N:将0.8g(1)中具有氧化性金属的CoMn-MOFs超声分在160mL水和160mL乙醇混合溶液中,随后将0.4g六亚甲基四胺充分溶解于上述溶液中,随后,在氮气保护下将上述溶液中放入微波反应器中在400W加热功率下于70℃反应2h,将反应后产物用乙醇或水清洗、干燥后即可得CoMn-MOFs-N。
(3)热解制备CoMn尖晶石催化剂:将(2)中CoMn-MOFs-N放入管式炉中,然后在空气的气氛下以2℃/min的升温速率升至400℃焙烧3h即可得到CoMn尖晶石催化剂。
对比例2
对比例2合成CeO2催化剂:与实施列1合成方法相同,不同之处在于合成过程没有添加具有氧化性MOFs,且氧化剂改为氧气;具体步骤如下:
0.3g Ce(NO3)3·6H2O超声分在160mL水和160mL乙醇混合溶液中,随后将0.4g六亚甲基四胺充分溶解于上述溶液中,随后,在氧气气氛下将上述溶液中放入微波反应器中在400W加热功率下于70℃反应2h,将反应后产物用乙醇或水清洗、干燥后即可得CeO2前驱体,将CeO2前驱体放入管式炉中,然后在空气的气氛下以2℃/min的升温速率升至400℃焙烧3h即可得到CeO2催化剂。
催化剂性能评价
采用固定床催化剂评价装置-在线气相色谱联用对实施例和对比例所合成的催化剂进行评价,具体步骤如下:准确称取0.1g催化剂装入5mm的石英管,然后放入反应炉中,在甲苯初始浓度为1000ppm以及5%vol水蒸气条件下,测量不同温度下出口甲苯浓度,以甲苯转化率为90%的温度作为催化剂活性评价标准,其结果如表1所示。
表1不同催化剂对甲苯的催化能耗
由表1可得实验例的T90%显著低于对比例,实施例1中制备的CoMn@CeO2-0.2催化剂对甲苯的T90%能够达到228℃,即本发明制备的催化剂较之常规催化剂能显著降低反应所需能耗,说明本发明设计的新制备途径能够通过有效调控异质结界面进而显著提高催化剂在催化氧化VOCs中低温活性,进而实现大大减少所需能耗的目的。
实施例1比表面略低于对比例1,说明MOFs在合成过程中起模板作用,进而可利用MOFs高比表面积提高所制备催化剂比表面积;实施例1-3中CeO2的粒径显著低于对比例2,说明本发明的方法能有效降低CeO2的粒径从而增加所形成异质结界面活性位点。
Claims (5)
1.一种尖晶石@CeO2催化剂,包括尖晶石和通过界面反应锚定在所述尖晶石表面上的CeO2颗粒,其特征在于:
所述尖晶石为具有氧化性金属的MOFs通过限域热解得到;
所述界面反应锚定CeO2过程是通过具有氧化性金属的MOFs与碱性条件下Ce3+发生氧化还原反应实现的;
所述氧化性金属为金属氰化物;
所述MOFs包括立方状的尖晶石和均匀分布在尖晶石上作为氧化位点的金属氰化物;
所述尖晶石@CeO2催化剂具有异质结结构,比表面积为133-296g/m2,其中二氧化铈的粒径大小为2.1~16.2nm。
2.一种尖晶石@CeO2催化剂的制备方法,步骤包括:
S1、通过共沉淀法合成具有氧化性金属的MOFs;
S2、保护氛围、微波加热下,通过氧化还原反应于S1得到的具有氧化性金属的MOFs的表面锚定CeO2颗粒,得到MOFs@CeO2;
S3、热解S2中MOFs@CeO2,生成具有异质结结构的尖晶石@CeO2催化剂;
其特征在于:
所述S1中,共沉淀法中使用的溶液包括溶液A和溶液B:
溶液A为:含过渡金属盐的水溶液,或含过渡金属盐和表面活性剂的水溶液;溶液B为:含金属氰化物的水溶液;
所述溶液A和溶液B的混合方法为:搅拌下,将溶液B逐滴加入溶液A,并持续搅拌0.2~3h;
所述共沉淀法老化参数为:室温下老化5~24h;
所述S2中,氧化还原反应中的还原物为:
由Ce(NO3)3·6H2O与NH3释放剂反应生成的Ce(OH)3;
微波加热的参数为:微波功率为400W~500W,反应温度为60℃~70℃,反应时间为2h~3h;
所述S3中,热解的参数为:空气气氛下,以1℃/min~2℃/min的升温速率升温至300℃~400℃,持续焙烧3-4h。
3.如权利要求2所述的一种尖晶石@CeO2催化剂的制备方法,其特征在于,所述制备方法包含的反应体系为体系A或体系B中的一个:
所述体系A中:
S1中:过渡金属盐为MnCl2·4H2O,金属氰化物为K3Co(CN)6;
S2中:NH3释放剂为六亚甲基四胺;
所述体系B中:
S1中:过渡金属盐为Ni(NO3)2·6H2O,表面活性剂为聚吡咯烷酮,金属氰化物为Na3Co(CN)6;
S2中:NH3释放剂为氯化铵。
4.如权利要求3所述的一种尖晶石@CeO2催化剂的制备方法,其特征在于:
所述体系A中:
S1中:过度金属盐与金属氰化物的摩尔比为10:28;
S2中:MOFs、Ce(NO3)3·6H2O和NH3释放剂的质量比为8:(2~3):4;
所述体系B中:
S1中:所述过渡金属盐、表面活性剂和金属氰化物的摩尔比为40:1:30;
S2中:MOFs、Ce(NO3)3·6H2O和NH3释放剂的质量比为10:2:7。
5.如权利1所述的尖晶石@CeO2催化剂的应用,其特征在于,能够用于催化氧化甲苯,催化效果为:
0.1g权利要求1中的尖晶石@CeO2催化剂,以甲苯转化率为90%的对应温度T90%作为催化剂活性评价标准,在甲苯初始浓度为1000ppm以及5%vol水蒸气条件下,其T90%为228℃。
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