TAP CHI HOA HOC T. 51(3) 269-272 THANG 6 NAM 2013
NGHIEN CU'U SU NGO DOC CCiA XUC TAG PEROVSKIT LaoySroaMnOj
TRONG P H A N CPNG OXI H O A H O A N T O A N m-XYLENTran Thj Thu Huyen
Vi^n Ky thudt Hda hoc. Trirdng Dgi liQC Bdch khoa Hd Ngi Den Toa soan 11 -6-2012
Abstract
The perovskite catalyst has a good catalytic activity in total oxidation of hydrocacbon, but that catalyst is often poisoned by HiO and SOi gases [4, 5]. So, il is necessary to prepare the perovskite catalysts which are not poisoned by H;0 and SO2 gases. We studied Ihe preparation and the catalytic properties of LaoySrojMnOj perovskile in total oxidation of m-xylene in previous reports [1,2] In present work, we continue studying of poisoning of Lan 7SrinMnOj perovskite catalyst in this reaction. From investigated results, it is demonstrated that the influence of ihe H2O gas on catalytic of Lao 7Sro jMnOj perovskite is only seen clearly from 200 tn 250''C temperature rang. The poisoning of LaoTSrosMnOs perovskite catalyst increases with increasing of SO2 gas strength, but this poisoning is temporary and the catalytic properties is restored as first after getting into contact wilh air.
1. MO DAU
Cac xuc tac perovskit cd hoat tinh cao trong phin img oxy hoi cic hydrocacbon, tuy nhien, chung lai cd nhugc diem de bj ngd dgc bdi hai nudc va S02 do tao thanh cic sunfat ben, khd bj phan huy nen da han che khi nang img dung cua loai xiic tac nay [4, 5]. Do vay, nghien ciru che tao xiic tac perovskit cd dp ben nhieL dg dn djnh cao va il bj ngp dpc bdi hai mrdc v i SO2 li can thiet. Xuc tic perovskit Lao.ySrojMnOj da dirge chimg tdi dieu che bang phirang phap sol-gel xitrat cho boat tinh cao trong phan ling oxy hoi hoan loan /»-xylen, cd dp ben nhiet vi do dn dinh tdt Iheo thdi gian d nhiet do phin ling thap (300**C) [1, 2]. Trong nghien ciiu niy, chung tdi tiep tuc nghien ciru sir ngd ddc ciJa xuc tac perovskit Lao.TSro.jMnOj trong mdi tru'dng cd mat ciia hai nudc va khi SO2.
2. THUC NGHIEM
Xuc tic dugc dieu che theo [1].
Hoat tinh cung nhu dp ben cua xiic tic Lao,7Sro,3Mn03 trong phan irng oxy hoa hoin loan m- xylen khi cd mat ciia hai nudc va khi SO2 dugc khao sat tren he phin ling vi ddng trong di6u kien thyc nghi?m: lugng xuc tic la 0,1 g; tdc dg ddng (luu lugng) li 2 lit/gid va dugc dinh gii thdng qua dp chuyen hoi a:
a{%) = 5„ - 5, <100 (1) S,
vdi So vi S| la dien tich ciia pic sac ky khi luong irng vdi cau tir i trudc phin ling (khdng cho qua chat xiic tie) vi sau khi da phan irng (da cho qua chit xuc lac).
- Phuang phip dau dpc hoi nudc: ddng khi phan irng dugc bd sung cac ham lugng hai nudc khic nhau (vdi luu lugng tdng 2 lit/gid) dugc khao sit do chuyen hoi va do ben xiic tac theo thai gian
- Phuang phap diu ddc khi SOi: diing phuang phap dau dgc tai chd: tirng lugng khi SO2 (vdi sd moi xic djnh) dugc bam vio ddng khi phan irng lai nhung thdi diem xac djnh. Dp chuyen hoi /H-xylen dugc do ngay sau 15 phut dau dpc SO2 d tirng thoi diem va khao sit dp ben xuc tic theo thdi gian sau khi bj dau ddc.
3. KET QUA
3.1. Khao sat sir ngo dgc xuc t i c perovskit LaAjSro^MnOj bdi hoi nu^c
3.LI. Anh hudng cua hdm luong hai nudc cd mat irong ddng khi phdn img den hogt tinh xuc tdc
Hinh 1 trinh bay anh hirdng ciia hai nudc cd mat trong ddng khi phan irng (vdi him lugng tii 4,14-
TCHH,T. 51(3),2013
12,17%) d8n ho^t linh xiic tic cua perovskit Lao.TSro.jMnOj.
Trdn Thj Thu Huyen
-4.14SKZO -7,28%K!0 ;
•12.17%«0 I
Nhlft 0« p h i n img (oC)
Hmh 1: Dg chuyen hoa /H-xylen tren xuc lac perovskit Lao.TSro.sMnOs vdi cac him lirgng hai nudc khac nhau
Cd the nhan thay, khi cd mat ciia hai nudc trong ddng khi phan irng, dp chuyen hoi m-xylen tren xiic tac perovskit Lao,7Sro.3Mn03 giam. Su giam nay chi the hien ro d viing nhi^t dg phan ung tir 200-250"C:
d 200°C khi CO mat 4,14% hai nudc trong ddng khi cho do chuyen hoa Hi-xylen khoang 35% va giam xudng cdn khoang 18% khi cd mat 12,17% hai nudc; d 250°C, dg chuyen hoa /H-xylen giim tir khoang 95% xudng cdn khoang 78% irng vdi ham lugng nudc trong ddng khi phan irng tir 4,14%i va 12,17%. 6 vitng nhiel do thip (100°C va 150°C) khi dd chuyen hoi nhd, chua thay ro sy anh hudng ciia hai nudc. Q nhiet dp phin ling cao (300''C), boat tinh xuc tac cung khdng bj bien ddi nhieu khi cd mat hai nudc (dp chuyen hoa wi-xylen dat khoing 96%
khi cd mat 12,17% hai nudc; khoing 98% vdi 7,28% hai nudc va gin nhu 100% d 4,14% hai nudc).
Sy anh hudng ciia hai nudc den ho?t tinh ciia xiic tic d cac nhiet dg khic nhau la do xay ra sy hip phy canh tranh giiJa /n-xylen va hai nudc: d vimg nhiet dp thap (lOCC va 150°C), /n-xylen bj hip phy tren be mat ciia perovskit vi da che phu hau het cic tam xiic tic nen nudc khdng the bj hap phu vao xuc lac dugc nira, khi dd, sy cd mat ciia hai nudc khdng anh den hoat tinh xuc tic; khi nhi^t do cao han (200- 250°C), m-xylen thoat dan ra khdi hk m$t ciia perovskit, khi do hai nudc cd mat se bj hap phy tren cac tam xuc lie lim giim ho^t linh ciia xiic lac; cdn khi nhiet dp phan umg cao len nua (SOCC), xiic tic
dugc hoat hoi tot, so tim boat tinh nhieu nen m§c dii hai nudc cd the bj hip phu cimg /n-xylen nhung van cho dg chuyen hoa dat gii tri cao va khong khac nhau nhieu. Nhu v^y, sy cd mat cua hai nudc tir 4,14-12,17% trong ddng khi phin ling chi giy sy giim hoat tinh xiic tac ciia perovskit chii yeu trong viing nhiet dg phan irng tir 200-250°C.
3.L2. Dg ben xuc tdc perovsku LaojSro^jMnOs khi cd mat hoi nudc
De kiem tra'dg ben ciia xuc tic khi cd m^t hoi nudc d nhiet dp phin img SOO^C, do do chuyen hoa m-xylen khi cd mit 12,17% hai nudc (!a him lugng nudc khio sit ldn nhat). Ket qua cho thay xuc tic perovskit LaojSro.jMnOs van cho dg ben cao, dp chuyen hoi van duy tri khoang 96% trong sudt 32 gid phin img lien tyc (hinh 2)
3.2. Khao sat su* ngQ d^c xiic tac perovskit LaojSfojMnOs bdi khi SOi
3.2.1. Anh hitung ciia lugng khi SO2 cd mgt trong ddng khi phdn ung sden hogt tinh xtic tdc
Hinh 3 mo t i sy bien thien dg chuyen hoa cua /H-xylen tren xuc tac perovskit Lao,7Sro.3Mn03 theo lugng SO2 khic nhau cd mat trong ddng khi phan ling sau 15 phiit diu dgc. Cac ket qui nay dugc liet ke trong bing 1.
Bdng T. Dp chuyen hoi ciia /?i-xylen tren xuc tac perovskit Lao,7Sro.3Mn03 trong mdi trudng cd SO2 vdi cac lugng khac nhau
Lucmg S O L I O ' (moi) Dp chuyen hoa sau 15 phiit dau doc (%)
0 100
0,06 98,4
0,11 96,3
0,34 87,7
0,89 77,4
3,21 i 4,29 61,4 47,9
6,43 35,1
7,50 25,6
TCHH,T. 51(3), 2013 Nghien cuu s\r ngg dgc ciia xuc tdc perovskit...
100 i-T-t-|-.-i---]
Thoi gian phan irng. h
Hinh 2: Bien thien ciia dg chuyen hoi //i-xylen theo thdi gian tren xiic tic Lao.7Sro3Mn03 khi cd m&t 12,17% hai nudc dnhi?tdg phan iing300°C Tir sd lieu d bang 1, cd the thay rang dg chuyen
hoa w;-xylen giam ro ret khi lugng khi SO2 cd m^t trong ddng khi phan irng tang len: khi cd mat 6^ IO'' moi SO2 trong ddng khi phan irng thi dp chuyen hoi /n-xylen hau nhu khdng bj thay ddi (chi giim tir 100% xudng cdn -98,4%); vdi 1,1x10"^ moi SO2 cung chi lim dp chuyen hoi giim khoang 4% (cdn ~
96,3%). Khi sd moi SO2 tang len nhieu nCra, xuc tie bj dau dgc mgnh han vi hoat tinh giim di ro ret. Vdi lugng SO2 la 7,5x10"^ moi, dp chuyen hoa giam cdn 25,6%. Nhu vgy, trong mdi trudng ciia khi thai neu CO mat khoang tir 6x10"^ den l,lx|0-^ moi SO2 thi cd the coi nhu chua anh hudng den linh chat xiic tie ciia perovskit Lao.7Sro,3Mn03.
10 12
Sd moi SO2X10'', moi Hinh 3: Dp chuyen hoi /)i-xylen tren xiic tie perovskit Lao,7Sro sMnOj trong mdi trudng cd mat SO2 vdi cac ham lugng khic nhau sau 15 phiit diu dgc De tinh sd lugng tam xuc tic bj diu ddc hoan
toin, keo dai dudng thang tren dd thj hinh 3, cat tryc hoinh tai diem img vdi sd moi SO2 li 1,03 x 10"^ moi, nghTa la sd moi xiic tic bj SO2 dau dpc cung li 1,03x10'^ moi, irng vdi so tim xiic tic perovskit Lao.7Sro.3Mn03 bj diu dpc la 6,204x10^" tam, Nhu vay, vdi 1,03x10"^ moi SO2 cd the dau dpc dugc hoan toan 6,204x 10^" tam hoat dgng xiic tic perovskit Lao.7Sro.3Mn03. Gii trj nay phii hgp vdi sd lugng tam xiic tic dj the thudng g|ip [3], 3.2.2. Dg ben xdc tdc LaojSrojMnOisau khi bi ngg dgc bai khi SO2 theo thdi gian phdn img
Do b6n cua xuc tie perovskit Lao,7Sro.3Mn03 theo thdi gian trong mdi trudng cd khi SO2 dugc khao sit vdi cic lugng SO2 khic nhau. Hinh 4 trinh biy bien thien do chuyen hoa theo thdi gian trong
phin ung oxy hoa m-xylen tren xiic tic perovskit LaojSrosMnOi d nhiet dp phan ling 300''C sau 15 gid phin ling Men tuc.
Cd the thay rang xiic tic perovskit Lao.ySrojMnOs hau nhu khdng bj ngd ddc bdi 6x10"^
moi SO2 (dp chuyen hoi giam khdng ding ke tir khoing 99% cdn khoang 97%i sau 18 gid phan irng lien tuc); vdi 8,9x10"^ moi SO2 lam do chuyen hoi /n-xylen giim tir 100% xudng cdn khoang 70%). Tuy nhien, sau khi bj ngd dpc, xiic tic cd do ben cao, gan nhu khdng bj thay ddi sau 15 gid phan ling lien tuc va dac biel sau khi dugc tiep xiic vdi khdng khi, hoat tinh ciia xiic tie lai dugc phuc hdi va cho dg chuySn hoa m-xylen trd lai nhu ban dau. Khi cd mat 7,5x10"* moi SO2, xiic tic bj diu dpc nhanh, dd chuySn hoi giim chi cdn khoang 26%i, sau dd theo thdi gian hoat tinh lai dugc phuc hdi dan va dat khoing 61% sau 15 gid phan irng lien tuc va sau khi
TCHH,T.51(3),2013 Trdn Thf Thu Huyin tiep xiic vdi khdng khi xiic tie dugc hoin nguyen lai
nhu ban dau.
100 -1 * * * — * * * w * * * * * * * * i
-7,5 10-4 moi S02 -8,93 10-6 molS02 - 5 6 10-6 moi S02
0 5 10 15 20 Thdi gian phan irng, h Hinh 4: BiSn thien dp chuyen hoi theo thdi gian
trong phan irng oxy hoa hoan loin »i-xylen tren xiic tac perovskit Lao,7Sn),3Mn03 khi cd mjt SOi
vdi Ciic krgng khic nhau d nhiet dg 300"C Nhu \ a;. xiic tic perovskit Lao.TSro ,Mn03 chi bi diu ddc tam thdi bdi SO2 ma cau true perovskit khdng bj phi huy sau phin ling. Ket qui phin tich
phd XRD cua perovskit Lao,7Sro.3Mn03 sau khi da xuc tic cho phan ling oxy hoa hoan toan /n-xylen vdi sy cd mat ciia khi SO2 trong ddng khi phin irng cho thay, ciu triic perovskit vln dugc gii? nguyen nhu ban diu mi khdng xuit hi?n cic pic nio khic dac trung cho cac pha I9, chirng td khong cd sy hinh thanh cua cac sunfat (hinh 5).
4. KET LUAN
- Anh hudng cua hai nudc den hoat tinh xiic tic CLia perovskit Lao,7Sro,3Mn03 chi thS hi?n ro d viing nhi?l dg tir 200-250^. C 300°C, xiic tic b6n va hau nhu khdng bj ngg dgc bdi hai nudc (vdi him lugng 12,17% hai nudc trong done khi phan ung).
Vdi phuang phip dau dpc tai cho, xiic tic perovskit Lao.7Sro.3Mn03 chi bj diu dgc tam thdi bdi SO2 vi sau khi bj diu dgc, xiic tic cd dg ben cao va die bi?t cd kha ning phuc hoi hoat tinh sau khi dugc tiep xuc vdi khdng khi.
Nhung ket qui nghien ciru nay cho thay kha nang irng dung vao thyc tien de xir ly cic d nhiem mdi trudng khi ciia cic perovskit la ldn.
I
Hinh 5: Gian dd nhieu xa tia X ciia xtic tic perovskit Lao,7Sro,3Mn03 sau khi da phan img trong mdi trudng cd m^t khi SO2 TAI LIEU THAM KHAO
! Tran Thj Thu Huyen. Nguyin Thi Minh Hi^n.
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