DSpace at VNU: Study on synthesis of Ni xZn 1-xAl 2O4 γ-Al 2O3 (x=0, 0.5, 1) spinel catalysts by hydrothermal method and their catalytic activity in aromatic hydrocarbon conversion

e-Journal of Surface Science and Nanotechnology 23 June 2012 Conference - IWAMN2009 - e-J Surf Sci Nanotech Vol 10 (2012) 259-262 Study on Synthesis of Nix Zn1−x Al2 O4 /γ-Al2 O3 (x=0, 0.5, 1) Spinel Catalysts by Hydrothermal Method and Their Catalytic Activity in Aromatic Hydrocarbon Conversion∗ Nguyen Thanh Binh, Hoa Huu Thu,† Le Thanh Son, Tran Thi Nhu Mai, and Nguyen Hong Vinh Department of Petroleum Chemistry, Faculty of Chemistry, Hanoi University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam (Received December 2009; Accepted 21 December 2011; Published 23 June 2012) The spinel oxides Nix Zn1−x Al2 O4 /γ-Al2 O3 (x = 0, 0.5, 1) were synthesized by hydrothermal method Oxides obtained were characterized by XRD and SEM The XRD result showed principal spinel phase over all samples In addition, NiO phase appeared for two cases of x = 0.5 and Using XRD results, the Rietveld Refinement method indicated that the sample ZnAl2 O4 /γ-Al2 O3 consisted of wt 80% of ZnAl2 O4 and 20% of γ-Al2 O3 with crystal size of 60 nm and 40 nm, respectively This one was in accordance with SEM image which showed quite uniform particles with the side from 50 to 80 nm Catalytic activity was evaluated by methylation of toluene by methanol and dehydrogenation of ethylbenzene to styrene For methylation reaction, the results showed high selectivity in xylene In case of Ni0.5 Zn0.5 Al2 O4 /γ-Al2 O3 , at 400◦ C, the result showed the best toluene conversion of 25.46% and selectivity in xylene was 88.33% In case of ethylbenzene dehydrogenation reaction, sample ZnAl2 O4 synthesized by coprecipitation method used as a reference catalyst We observed, after 180 of time reaction, a double conversion of ethylbenzene on ZnAl2 O4 /γ-Al2 O3 in comparison with ZnAl2 O4 reference In addition, working time of ZnAl2 O4 /γ-Al2 O3 was longer than this one of ZnAl2 O4 reference [DOI: 10.1380/ejssnt.2012.259] Keywords: Nano spinel; Ethylbenzene; Dehydrogenation I INTRODUCTION Spinels are blulk catalysts that have small total surface area [1] But they have high thermal, hydrothermal stability, and acid, base, mechanical resistance The most advantage of spinels that they are able to form the solid solution with active components can be changed easily [1] In fact, the spinels that active components are transition metallic oxides usually present high catalytic activity in oxidation reactions Spinels were synthesized by many techniques For example, the ancient techniques as coprecipitation of mixture of metallic ions or by solid state reaction of mixture of metallic oxides formed spinels with large crystal size and small total surface area [2–4] Recently, the spinels were synthesized by new techniques as sol-gel techniques, hydrothemal method or decomposition of complexes as precursors showed that obtained spinels had nano-crystal size and large total surface area [5, 6] We synthesized three catalyst samples Nix Zn1−x Al2 O4 /γ-Al2 O3 (x = 0, 0.5, 1) by hydrothermal method using active gel Al(OH)3 that obtained from neutralization a solution of aluminum nitrate by ammoniac and acetates of bivalent metals, as Ni 2+, Zn2+ During the treatment in an autoclave at 250◦ C, the ions of bivalent metals form the precursors Al–O–M (M=Ni, Zn) after the reaction: Al ≡ Al–O–H + M2+ + CH3 COO− ⇌ ≡ Al–O–M(precursor) + CH3 COOH ZnAl2O4 ZnAl2O4/g-Al2O3 (1) Concurrently, in these conditions ion nitrate in solution oxidize the acetic acid formed to help this chemical equi- ∗ This paper was presented at the International Workshop on Advanced Materials and Nanotechnology 2009 (IWAMN2009), Hanoi University of Science, VNU, Hanoi, Vietnam, 24-25 November, 2009 † Corresponding author: hoahuuthu@yahoo.com Ni0.5Zn0.5Al2O4/g-Al2O3 Figure 1: SEM images of catalysts The SEM images of catalysts shower particle size distribution of these catalysts was FIG 1: SEM images of catalysts g g g libriumg to move to right forming precursors When the precursors were calcined at 600◦ C, spinel phases on γAl2 O3 was formed g II EXPERIMENTAL A solution of aluminum nitrate 1.5 M was neutralized by ammonia solution to pH = 5.5-6 In the obtained gelatinous precipitate, the zinc acetate and nickel acetate were dissolved with ratios calculated The mixture was stirred and treat at 250◦ C in an autoclave for 15 h Obtained precursors were washed with water distillated, dried at 160◦ C for 12 h, then obtained solids were calcined at 600◦ C for h to form catalysts Used catalysts had particle size of 0.5-1 mm The phase composition and the structure of the catalysts were analyzed by XRD using SIEMEN D5005 Diffractometer with Cu Kα radiation (λ = 1.5406 ˚ A) The calculation of content of crystal phases and crystal size by Rietveld Refinement method using Fullprof 200 and BGMN software based on RXD results of ZnAl2 O4 /γAl2 O3 sample was carried out according to Ref [7] The observation of the catalysts surface and estimation particle size of catalysts were using SEM-5410LV with the enlargement of 20000 times The influence of reaction temperature and catalyst c 2012 The Surface Science Society of Japan (http://www.sssj.org/ejssnt) ISSN 1348-0391 ⃝ 259 Nguyen, et al Volume 10 (2012) Figure Results of calculation content of crystal crystal phase size of ZnAl FIG 2: 2: Results of calculation of content ofof crystal phase and size of ZnAl2 Oand by Rietveld Refinement /γ-Alcrystal O3 sample method using Fullprof 2000 and BGMN software RESULTS AND DISCUSSIONS The SEM images of catalysts were represented in Fig The SEM images of catalysts shower particle size distribution of these catalysts was quite uniform Estimation of particle size in samples synthesized by hydrothermal method from 50 nm to 80 nm For the sample obtained by coprecipitation, particle size was approximately 130 nm We have recorded XRD patterns of the catalysts The XRD patterns of catalysts confirmed that spinel phases and γ-Al2 O3 phase were formed very well For Ni0.5 Zn0.5 Al2 O4 /γ-Al2 O3 and NiAl2 O4 / γ-Al2 O3 samples, beside spinels and γ-Al2 O3 phases, formation of NiO phase was observed On XRD patterns of catalysts, an enlargement of picks was observed This effect was generated by small crystal size The results of calculation of content of crystal phases 260 25 20 15 10 0 10 20 30 40 50 60 70 80 90 100 Content Zn (%) tent in catalysts at reaction temperature FIG 3:reaction Influence yield of Zn content in catalysts reaction of yield at reaction temperature of 400◦ C and crystal size of ZnAl2 O4 /γ-Al2 O3 sample by Rietveld refinement method using fullprof 2000 and BGMN software was shown in Fig The result showed that this sample consisted of 80% of NiAl2 O4 with crystal size of 60 nm, and 20% of γ-Al2 O3 with crystal size of 40 nm This result was corresponding to SEM images of the catalysts The results of study on methylation of toluene by methanol were shown in Figs 3, and The results showed that xylene was formed with high selectivity When increasing the reaction temperature, the conversion of toluene increased selectivity Figure but 5: the Influence of temperature of xylene decreased Methylation reaction of toluene on catalysts Ni on Ni0.5 Zn0.5 Al2 O4 /γ-Al2 O3 showed the highest toluene conversion of 25.46% with xylene selectivity of 88.33% at 400◦ C, a little amount of benzene and trimethylbenzene was formed from secondary reactions The composition of catalysts also influenced on catYield H (%) III 30 Yield H(%) composition to catalytic activity were investigated using methylation of toluene by methanol Reaction were carried out in a reactors of gaseous phase, reaction temperature from 290-400◦ C, volume rate of toluene of 2.5 h−1 , ratio of reagents of: toluene: methanol: water= 1:4:1.5, after 30 minutes the products were taken out to analyze by GC-MS The comparison of catalysts activity of ZnAl2 O4 /γAl2 O3 sample and ZnAl2 O4 sample synthesized by coprecipitation, and influence of reaction time to catalytic activity were carried out using oxidation dehydrogenation of ethybenzene to styrene using oxygen of air The reaction was carried out at 450◦ C, volume rate of h−1 , rate of air flow of 10 ml/minute The liquid products were analyzed using GCMSHP6890 equipment with HP5 capillary column, carrious gas of helium, MS detector, temperature of column top was 50◦ C, temperature of column end was 270◦ C http://www.sssj.org/ejssnt (J-Stage: http://www.jstage.jst.go.jp/browse/ejssnt/) e-Journal of Surface Science and Nanotechnology Volume 10 (2012) 100 40 90 35 80 30 Conversion(%) Selectivity S(%) 70 60 50 40 ZnAl2O4/g-Al2O3 25 20 15 ZnAl2O4 30 10 20 10 0 10 20 30 40 50 60 Content Ni (%) 70 80 90 100 20 40 60 80 100 120 140 160 180 200 Time (mins) tent in catalysts Figure 4: Influence of Ni content in catalysts Influence of at Nireaction contenttemperature in catalystsofreaction temperatureFIG of 4:reaction yield 400 C yield at ◦ reaction temperature of 400 C ence of reaction time to styrene FIG 6: Influence of reaction time to styrene selectivity on catalysts ZnAl2 O4 /γ-Al2 O3 and ZnAl2 O4 30 100 / -Al2O3 g Ni0.5Zn0.5Al2O4/g-Al2O3 / -Al2O3 20 15 ZnAl2O4/g-Al2O3 / -Al2O3 ZnAl2O4 10 Conversion (%) 90 Conversion(%) Yield H (%) ZnAl2O4 95 25 85 80 ZnAl2O4/g-Al2O3 75 70 65 Temperature 200( C) 250 300 350 400 450 o 500 g 60 50 100 150 200 Temperature ( C) re 5: Influence of temperature to reaction Time (min) Figure 5: Influence O of andtemperature to reaction ence/Al of reaction O and time to styrene Figure 7: Influence of reaction time to ethylbenzene conversion on catalysts FIG 5: Influence of temperature to reaction yield on catalysts Ni0.5 Zn0.5 Al2 O4 /Al2 O3 and ZnAl2 O4 /Al2 O3 FIG 7: Influence of reaction time to ethylbenzene conversion on catalysts ZnAl2 O4 /γ-Al2 O3 and ZnAl2 O4 g g alytic activity Figure showed influence of Zngcontent in g secondary reactions involving cracking reaction, dealkycatalysts to reaction yield, at temperature of 400◦ C (Zn lation conducting to form little amount of benzene, bencontent = nZn /(nZn +nNi ) A maximum yield attained on g zaldehyde, benzofurane as second products observed on Ni0.5 Zn0.5 Al2 O4 /γ-Al2 O3 catalysts at Zn content of 54% GCMS diagram The cock content on ZnAl2 O4 /γ-Al2 O3 Increasing of Ni content in catalysts effected to decrease sample was of 85.8 mg/1g catalyst, on ZnAl2 Og4 sample xylem selectivity, and increase content of secondary prodwas 57.9 mg/1g catalyst after h of reaction ucts from parasite reaction Figure showed influence of Ni content in catalysts on selectivity of xylene, at temperature of 400◦ C The results showed that when the absence g IV CONCLUSION of water in the first material, the conversion of toluene was very low, about 8.14% on Ni0.5 Zn0.5 Al2 O4 /γ-Al2 O3 cataThe catalysts of spinels on gamma aluminium oxide lysts at 400◦ C This permitted to predict that alkylation of toluene was mainly catalyzed by OH groups link with - Nix Zn1−x Al2 O4 /γ-Al2 O3 (x = 0, 0.5, 1) were synthemetal ion as Bronsted acid centers that the water had the sized using hydrothermal method XRD patterns of catalysts confirmed that spinel phases and gγ-Al2 O3 phase role to form them The results of study on oxidative dehydrogenation of were formed very well g Calculation of content of crystal phases and crystal size ethylbenzene to styrene were represented in Figs and The results showed that styrene selectivity was very high by Rietveld Refinement method using Fullprof 2000 and on both of two samples The ethylbenzene conversion on BGMN software based on XRD results of ZnAl2 O4 /γZnAl2 O4 /γ-Al2 O3 sample was about two times more than Al2 O3 sample showed that this sample consisted of 80% on ZnAl2 O4 sample synthesized by coprecipitation after of ZnAl2 O4 with crystal size of 60 nm, and 20% of γreact time of 180 minutes This can be explained by small Al2 O3 with crystal size of 40 nm These results were crystal size and large total surface area of ZnAl2 O4 /γ- corresponding with SEM images Al2 O3 sample For methylation of toluene by methanol on catalysts, The catalytic activity decreased slowly according to xylene was formed with high selectivity Ni content in the reaction time ZnAl2 O4 /γ-Al2 O3 sample contained catalysts influenced to toluene conversion and xylene seAl2 O3 as solid acid and it had porous structure effected lectivity http://www.sssj.org/ejssnt (J-Stage: http://www.jstage.jst.go.jp/browse/ejssnt/) 261 Nguyen, et al Volume 10 (2012) For oxidation dehydrogenation of ethylbenzene to styrene, ZnAl2 O4 /γ-Al2 O3 sample was better than ZnAl2 O4 sample synthesized by coprecipitation with higher catalytic activity and longer life time These results contributed to study to synthesize and catalytic activity of nanostructure materials [1] P V Tuong, Inorganic Materials (Editor of Vietnam National University in Hanoi, Hanoi, 2002) [2] B Gillot, A Ruosset and G Dupre, Solid State Chem 25, 263 (1978) [3] M Bremer, S Fischer, and N Langbein, Thermochimica Acta 209, 323 (1992) [4] J I Dicosimo, J Catal 178, 499 (1998) 262 Acknowledgments The authors gratefully acknowledge financial support from the National Foundation for Science and Technology Development of Vietnam (NAFOSTED) [5] H Heegn, J Cryst Res Technol 35, 255 (2000) [6] Y Xie, J Mater B 34, L1 (1995) [7] J Rodriguez-Carvajal, An Introduction to the Program FULLPROF 2000 (Laboratoire Leon Brillouin (CEA CNRS), France, 2001) http://www.sssj.org/ejssnt (J-Stage: http://www.jstage.jst.go.jp/browse/ejssnt/) ... in catalysts Figure 4: Influence of Ni content in catalysts Influence of at Nireaction contenttemperature in catalystsofreaction temperatureFIG of 4:reaction yield 400 C yield at ◦ reaction temperature... on Ni0 .5 Zn0.5 Al2 O4 /γ-Al2 O3 cataThe catalysts of spinels on gamma aluminium oxide lysts at 400◦ C This permitted to predict that alkylation of toluene was mainly catalyzed by OH groups link... from secondary reactions The composition of catalysts also in uenced on catYield H (%) III 30 Yield H(%) composition to catalytic activity were investigated using methylation of toluene by methanol