Fuel 92 (2012) 373–376

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Fuel

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Short communication

Trace precious metal Pt doped plate-type anodic alumina Ni catalystsfor methane reforming reaction

Lu Zhou ⇑, Yu Guo, Jian Chen, Makoto Sakurai, Hideo KameyamaDepartment of Chemical Engineering, Faculty of Engineering, Tokyo University of Agriculture and Technology, 24-16 Nakacho 2, Koganei-Shi, Tokyo 184-8588, Japan

a r t i c l e i n f o

Article history:Received 21 November 2010Received in revised form 18 June 2011Accepted 20 June 2011Available online 23 July 2011

Keywords:ReformingAlumite supportMethaneDaily start-up and shut-down

0016-2361/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.06.039

⇑ Corresponding author.E-mail address: zhoulu1104@gmail.com (L. Zhou).

a b s t r a c t

A novel plate-type anodic alumina supported 17.9 wt% Ni/Al2O3/alloy showed a quick deactivation indaily start-up and shut down (DSS) steam reforming of methane (SRM) at 700 �C, because of the Ni oxi-dation reaction with steam. When 0.078 wt% Pt was doped, the catalyst exhibited self-activation and self-regeneration ability, while 3000 h continual and 500-time DSS stability was testified. Further, this Pt–Nicatalyst also showed excellent reactivity during carbon dioxide reforming of methane (CMR) and partialoxidation of methane reaction (POM). According to the TPR and XRD analyses, the H2 spillover effect andthe formation of Pt–Ni alloy were believed to be the main reason for the reactivity improvement of thiscatalyst.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

In our previous study [1–4], a plate-type anodic aluminasupported alumite Ni catalyst, 17.9 wt% Ni/Al2O3/alloy, wasprepared by impregnation method. This catalyst exhibited favoriteactivity and stability during a stationary SRM testing at 700 �C,F/W = 157,000 mL/(h gcat). The methane conversion was kept at97% near equilibrium value, while no deactivation was found dur-ing a period of 100 h. But, when subjected to a DSS SRM mode thatwould be adopted for domestic fuel cells, this Ni-based catalyst en-tirely deactivated after the steam purging [4]. It was found that thesteam purge at 700 �C resulted in the Ni oxidation and thus a re-reduction with H2 was required to regenerate the catalyst [1].However, this would never be available for a common family tointroduce H2 gas into the reformer to re-activate the catalyst, con-sidering the cost and safe of the fuel cell system. Thus, a catalysttolerable for stationary and DSS SRM is required. In literatures[5–8], in order to suppress Ni oxidation, Ni catalysts are alwaysmodified with precious noble metal such as Ru, Pt and Rh in viewof their hydrogen spillover function. According to Miyata et al. [9],among these noble metals, the Rh and Pt seemed to showed thebest performance as only 0.1 wt% addition was required to sustaina 16.0 wt% Ni/Mg(Al)O catalyst reactivity during the DSS SRM,while as more as 0.5 wt% Ru or Pd addition was essential.

In these contributions, the effect of Pt doping (The Rh was notconsidered due to its high cost) over the 17.9 wt% Ni/Al2O3/alloywas investigated in our research. It was found that the 0.079 wt%

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Pt doped 17.9 wt% Ni/Al2O3/alloy catalyst showed stable activityduring 700 �C, 800 �C and even 900 �C steam-purge DSS SRM, whilethe pre-reduction with H2 was not necessary. With the cooperationwith TOKYO GAS Co., Ltd., this Pt–Ni catalyst showed a 3000 h con-tinual and 500-time DSS SRM stability at 680 �C, F/W = 34,000mL/(h gcat). This catalyst was also demonstrated to be applicablefor CRM and DPOM.

2. Experimental method

A commercial plate Al/Cr–Ni-alloy/Al clad base material with anAl layer thickness of 45 lm and a Cr–Ni-alloy layer thickness of85 lm (Daido Steel Co., Ltd.) was used to prepare the catalyst.The 17.9 wt% Ni/Al2O3/alloy was prepared by impregnation meth-od with Ni(NO3)2�6H2O precursor. Details could be referred to [3].Pt was doped by impregnating the 17.9 wt% Ni/Al2O3/alloy withH2PtCl6 solution. The sample was then dried at 120 �C overnightand calcined at 500 �C for 3 h. Metal loadings were analyzed withan inductively coupled plasma spectrometer (ICPS-7510, ShimadzuCorp.). The morphology of the catalysts was examined by fieldemission scanning electron microscope (FE-SEM) (S-4800, Hitachi,Ltd.). H2-TPR with 65% H2/Ar analysis was performed on ChemBET3000 (Quantachrome Instruments, Co.). Details are available in [3].SRM tests were carried out in a plug flow integrated reactor (i.d.10 mm) under atmospheric pressure by cutting the plate catalystinto small pieces. N2 was introduced as the inner inference gasfor GC analyses. In all SRM tests, the ratio of CH4/H2O/N2 in the feedgas was controlled at 1:3:2, while the CH4 feed flow was fixed at50 mL/min (i.e. F/W = 157,000 mL/(h g)). During the DSS SRM, the

Fig. 1. The DSS SRM over 17.9 wt% Ni/Al2O3/alloy and 0.079 wt% Pt doped 17.9 wt%Ni/Al2O3/alloy at 700 �C, S/C = 3, F/W = 157,000 mL/h gcat. (a) 17.9 wt% Ni/Al2O3/alloy; (b) 0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloy reduction condition: (a)800 �C H2-reduction for 0.5 h; (b) without H2 reduction.

Fig. 2. XRD and TPR analyses over 17.9 wt% Ni/Al2O3/alloy and 0.079 wt% Pt doped17.9 wt% Ni/Al2O3/alloy at 700 �C during DSS SRM. (a) 17.9 wt% Ni/Al2O3/alloy after700 �C steam-purge DSS SRM; (b) 0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloy after700 �C steam-purge DSS SRM; (c) 0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloyafter SRM at 700 �C, S/C = 3, F/W = 157,000 mL/h gcat without pre-reduction.

374 L. Zhou et al. / Fuel 92 (2012) 373–376

catalyst was purged by steam at 700 �C. The pre-reduction wasconduced with 100 mL/min H2 at 800 �C for 0.5 h. The dry outletgases were analyzed by an on-line gas chromatograph (GC-2014AT, Shimadzu Corp.). The results obtained were evaluated interms of CH4 conversion.

3. Results and discussion

3.1. SRM over 0.079 Pt wt% doped 17.9 wt% Ni/Al2O3/alloy

In Fig. 1, the 17.9 wt% Ni catalyst deactivated entirely after700 �C steam purge. However, after added with 0.078 wt% Pt overthis Ni catalyst, it showed an excellent DSS SRM reactivity under700, 800 and even 900 �C steam purging. Moreover, it was foundthat the Pt doped Ni catalyst could activate itself, because a 97%methane conversion was achieved by subjecting the fresh catalystto the SRM at 700 �C in Fig. 1 without pre-reduction with H2.

The TPR and XRD analyses over the fresh and deactivatedsamples in Fig. 1 were conducted in Fig. 2. Compared to the TPRprofiles of Pt doped Ni and Ni only catalyst, negligible reductionpeak was shown in both anodic alumina support and 0.079 wt%Pt/Al2O3/alloy. For the 17.9 wt% Ni/Al2O3/alloy catalyst, althougha H2 pre-reduction was conducted before SRM test, the 700 �Csteamed catalyst showed the consumption of H2 in TPR(peaks <500 �C were assigned to NiO, peaks between 500 and 700were NiOx, peaks >700 �C were NiAl2O4), revealing the oxidationof Ni0 with steam into Ni2+ during steam purging. On the otherpart, for the 0.079 wt% Pt doped 17.9 wt% Ni catalyst, both freshand 700 �C steamed catalysts showed similar TPR profiles to thatof 17.9 wt% Ni/Al2O3/alloy catalyst. But, it should be noted thatby doping Pt, the reduction temperature of both fresh and steamedcatalysts were shifted to a lower temperature. Moreover, the XRDanalyses over the spared samples after DSS SRM showed the obvi-ous existence of Ni0 over Pt doped Ni catalyst, whilst only hard-to-reduce Ni2+ species over Ni only catalyst. These concluded thatthe doped Pt could re-reduce the oxidized Ni. In order to testify thisconclusion, a SRM test over Pt doped Ni was conducted withoutpre-reduction. The result showed a 97% methane conversion byintroducing reactant gas at 700 �C. The XRD results showed theNi0 existence over the spared catalyst. Meanwhile, although benegligible, the Ni0Pt peaks were also found over Pt doped Ni sam-ples. We considered this as the peak of Pt–Ni alloy. Li et al. also sta-ted that the addition of noble metals on Ni would make a stronginteraction between Ni and noble metals.

As to the function of Pt doping for the DSS SRM, it was proposedas follows. When fresh or steamed Pt-doped catalysts were sub-jected to the flow of CH4 and steam, we considered that Pt cata-lyzed CH4 reforming reaction at 700 �C initiated the reduction ofthe catalyst. As a result of CH4 reforming reaction, the hydrogenproduced and spilled to reduce Ni2+ species. Further reduction ofPt–Ni-oxide clusters would be facilitated by increased availabilityof the hydrogen produced from the Ni catalyzed CH4 reformingreaction followed by the water gas shift reaction between CO andexcess H2O. According to these, the Ni2+ on this catalyst was re-duced by hydrogen spillover from Pt, while Pt–Ni was formed onthe surface of metallic Ni particles.

Furthermore, in Fig. 1, for Pt doped Ni catalyst, although the cat-alyst showed stable DSS SRM reactivity under all temperatures, itcould be seen that with the increase of steam purging temperature,more time was required for the totally recovery of methane con-version, as only 10 min for 700 �C, 30 min for 800 �C and 60 minfor 900 �C steam purging DSS SRM. As we known, the higher tem-perature steaming the Ni catalyst was subjected to, the more se-vere oxidation and especially the sintering of Ni would beexpected. But, it should be noted that none nickel oxides peakwas detected over the Pt doped Ni catalysts by restarting theSRM over the steamed catalysts. This means that the amount ofhydrogen spilled from the doped Pt is enough to reduce the nickeloxides over the steamed catalysts. Therefore, the differences ofself-regenerative time among different temperatures must referto the Ni sintering. Zhan et al. [10] found that by doping 0.1 wt%Pt over a 16.0 wt% Ni/Mg(Al)O catalyst, the nickel particles overthis catalyst showed self-redispersion ability, that is, althoughthe nickel particles were sintered from the 6.5 nm to the 21.9 nmafter the 900 �C steam purge for 10 h in a H2/H2O/N2 (20/100/25 mL/min), by subjecting to the 700 �C SRM again, the Ni particlessize decreased from 21.9 nm to 14.5 nm. Zhan et al. ascribed this tothe formation of Pt–Ni alloy. Possibly, similarly to Zhan et al., ourPt doped Ni catalyst might have the same self-redispersion ability,while the time needed for the Pt doped Ni catalysts to regeneratetheir initial SRM reactivity in Fig. 1 could be considered as the Niparticles re-dispersion time. Also, by comparing the FE-SEM

Fig. 3. Continual and DSS SRM with 13A city gas over 0.079 wt% Pt doped 17.9 wt%Ni/Al2O3/alloy. Reaction condition: without pre-reduction, 680 �C, S/C = 3, F/W = 34,000 mL/h gcat.

Fig. 4. POM and CMR test over 0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloy. POMtest: without pre-reduction, 800–400 �C, CH4/O2 = 2, F/W = 58,875 mL/(h gcat); CMRtest: without pre-reduction, 700 �C, CH4/CO2 = 1, F/W = 78,900 mL/(h gcat).

L. Zhou et al. / Fuel 92 (2012) 373–376 375

between the steamed catalyst and the DSS SRM steamed catalyst,the re-dispersion was showed. While the mechanism of the self-redispersion was still unknown, it was considered as follows: Ni0

is oxidized incorporated into the alumina layer under steam purge,whereas the Ni2+ is released as small Ni0 particles on the catalystsurface by the spilled hydrogen from methane.

3.2. Life test of 0.079 Pt wt% doped 17.9 wt% Ni/Al2O3/alloy for SRM

As to the industrial application of our alumite SRM catalysts,through the cooperation with TOKYO GAS Co., Ltd., a life test of0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloy catalyst for the SRMwas conducted with the usual Japanese city gas (13A). The compo-sition of the city gas was mainly 89.60 vol.% CH4, 5.62 vol.% C2H6,3.43 vol.% C3H8 and 1.35 vol.% C4H10. Little deactivation was foundduring 3000 h continual SRM and 500-time DSS SRM in Fig. 3,which indicated the application possibility in fuel cells.

3.3. POM and CMR over 0.079 Pt wt% doped 17.9 wt% Ni/Al2O3/alloy

SRM conducted over Ni catalysts were mainly considered in thisresearch to provide H2 for domestic fuel cells. However, this pro-cess is energy intensive. Catalytic partial oxidation of methane(POM) is a potential alternative to SRM as a route to provide hydro-gen [11]. Compared with SRM, POM is a mildly exothermic process(CH4 + 1/2O2 ? CO + 2H2 DH298 = �36 kJ/mol), which does notneed energy to input. On the other hand, carbon dioxide reformingof methane (CMR) to produce synthesis gas attracts manyresearchers for the chemical utilization of natural gas and carbondioxide, which are suspected to be greenhouse gases. The majorinterest in CMR originates from the demand of the production ofliquid hydrocarbons and oxygenates, e.g. acetic acid, formaldehyde,and oxoalcohols since this reaction gives synthesis gas with a H2/CO ratio of about 1 [12]. According to literature [13–15], althoughNi-based catalysts could catalyze both POM and CMR, almost allkinds of Ni catalysts, e.g. Ni–La2O3, Ni/MO (M = Al, Si, Zr, etc.),Ni–Mg–O, etc., suffered more or less from the disadvantage ofserious deactivation caused by fouling to coke. For this reason, anumber of studies have been focused on the development of acoke-resistant catalyst. The catalysts based on noble metals havebeen found to be less sensitive to carbon deposition. However,considering the high cost and limited availability of noble metals,it is more practical in industrial standpoint to develop Ni-based

catalysts with high performance and high resistance to carbondeposition.

Regarding to the high coke-resistant of the anodic Ni catalyst[2] and the unique Pt–Ni alloy over Pt doped catalyst, in this re-search, the POM and CMR were also conducted with the SRMequipment over a 0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloy.No pre-reduction treatment was applied for both POM and CMR.100 mL/min N2 was used as a carrier gas, while the mole ratio ofCH4/O2 was controlled at 2 and the F/W was fixed at 58,875 mL/(h gcat) for POM, while the ratio of reactant gas CH4/CO2 was con-trolled at 1:1 and the F/W was fixed at 78,900 mL/(h gcat). Fromthe result in Fig. 4, the Pt doped Ni catalyst performed good POMreactivity while stable methane conversion almost near equilib-rium value was achieved at every stage of temperature. For theCMR test, although both CH4 and CO2 conversion were c.a. 10–20% lower than the equilibrium value, a stable CRM reactivity interms of 70% CH4 conversion and 73% CO2 conversion was achievedover the catalyst at 700 �C for as long as 90 h. These concluded amultiple application of this 0.079 wt% Pt doped 17.9 wt% Ni/Al2O3/alloy catalyst.

Some relevant literatures attributed the excellent coking resis-tance to a higher saturation concentration of carbon in the smallernickel crystals. That is, a small crystal size results in a large satura-tion concentration leading to a low driving force of carbon diffu-sion and hence a lower coking rate. Guo et al. [16] reported thatthe high stability of the Ni/MgAl2O4 catalyst could be attributedto the interaction between Ni and the support, which results inhighly dispersed Ni particles that are resistant to carbon depositionand sintering. These results seemed to suggest the importance ofkeeping small Ni particle size. Because of the re-dispersion effectof Pt–Ni alloy, the Ni particles could be maintained as small en-ough to be tolerable for the coking.

4. Conclusions

By the addition of trace amount of 0.079 wt% noble metal Pt, thealumite Ni catalyst showed stable DSS SRM reactivity, even with-out pre-reduction. The H2 spillover function and formation ofPt–Ni alloy was thought to re-activated and re-disperse thesteamed catalyst. Over this catalyst, a stable 3000 h continuallySRM and a 500-time DSS SRM reactivity was confirmed underthe 13A city gas. Moreover, it was found this catalyst would bemultiple applicable, because excellent POM and CMR reactivitywere also achieved over this catalyst.

376 L. Zhou et al. / Fuel 92 (2012) 373–376

Acknowledgment

This work was supported by the TOKYO GAS Co., Ltd. of Japan.

References

[1] Guo Y, Tran TP, Zhou L, Zhang Q, Kameyama H. Steam methane reformingusing an anodic alumina supported nickel catalyst (Ni/Al2O3/alloy): analysis ofcatalyst deactivation. J Chem Eng Jpn 2007;40:1221.

[2] Zhou L, Guo Y, Zhang Q, Tran T P, Sakurai M, Kameyama H. A plate-type anodicalumina supported nickel catalyst for methane steam reforming. J Chem EngJpn 2008;41:90.

[3] Zhou L, Guo Y, Zhang Q, Yagi M, Hatakeyama J, Li H B, et al. A novel catalystwith plate-type anodic alumina supports, Ni/NiAl2O4/c-Al2O3/alloy, for steamreforming of methane. Appl Catal A 2008;347:200.

[4] Zhou L, Guo Y, Yagi M, Sakurai M, Kameyama H. Investigation of a novel porousanodic alumina plate for methane steam reforming: hydrothermal stability,electrical heating possibility and reforming reactivity. Int J Hydrogen Energy2009;34:844.

[5] Jeong JH, Lee JW, Seo DJ, Seo Y, Yoon WL, Lee DK, et al. Ru-doped Ni catalystseffective for the steam reforming of methane without the pre-reductiontreatment with H2. Appl Catal A 2006;302:151.

[6] Li D, Shishido T, Oumi Y, Sano T, Takehira K. Self-activation and self-regenerative activity of trace Rh-doped Ni/Mg(Al)O catalysts in steamreforming of methane. Appl Catal A 2007;332:98.

[7] Mukainakano Y, oshida KY, kadoa S, Okumura K, Kunimori K, Tomishige K.Catalytic performance and characterization of Pt–Ni bimetallic catalysts foroxidative steam reforming of methane. Chem Eng Sci 2008;63:4891.

[8] Suzuki T, Iwanami H, Yoshinari T. Steam reforming of kerosene on Ru/Al2O3

catalyst to yield hydrogen. Int J Hydrogen Energy 2000;25:119.[9] Miyata T, Li D, Shiraga M, Shishido T, Oumi Y, Sano Y, et al. Promoting effect of

Rh, Pd and Pt noble metals to the Ni/Mg(Al)O catalysts for the DSS-likeoperation in CH4 steam reforming. Appl Catal A 2006;310:97.

[10] Zhan Y, Li D, Nishida K, Shishido T, Oumi Y, Sano T, et al. Citrate orhydrotalcite? As the precursor of Pt or Ru-doped Ni/Mg(Al)O catalyst forpropane oxidative reforming. Appl Catal A 2009;356:231.

[11] Chen P, Zhang H, Lin G, Tsai K. Development of coking-resistant Ni-basedcatalyst for partial oxidation and CO2-reforming of methane to syngas. ApplCatal A 1998;166:343.

[12] Wang Y, Liu H, Xu BJ. Durable Ni/MgO catalysts for CO2 reforming of methane:activity and metal–support interaction. Mol Catal A 2009;299:44.

[13] Nakamura J, Aikawa K, Sato K, Uchijima T. Role of support in reforming of CH4

with CO2 over Rh catalysts. Catal Lett 1994;25:265.[14] Chang J, Park S, Chon H. Catalytic activity and coke resistance in the carbon

dioxide reforming of methane to synthesis gas over zeolite-supported Nicatalysts. Appl Catal A 1996;145:111.

[15] Ruckenstein E, Hu Y. CO2 reforming of CH4 over Ni/alkaline earth metal oxidecatalysts. Appl Catal A 1998;51:183.

[16] Guo J, Lou H, Zhao H, Chai DF, Zheng XM. Dry reforming of methane over nickelcatalysts supported on magnesium aluminate spinels. Appl Catal A2004;273:75.