Daily Start-up And Shut-down Research Articles

Improving the Stability of Ru-Doped Ni-Based Catalysts for Steam Methane Reforming during Daily Startup and Shutdown Operation

In this study, a Ru-doped Ni pellet-type catalyst was prepared to produce hydrogen via steam methane reforming (SMR). A small amount of Ru addition on the Ni catalyst improved Ni dispersion, thus affording a higher catalytic activity than that of the Ni catalyst. During the daily startup and shutdown (DSS) operations, the CH4 conversion of Ni catalysts significantly decreased because of Ni metal oxidation to NiAl2O4, which is not reduced completely at 700 °C. Conversely, the oxidized Ni species in the Ru–Ni catalyst can be reduced under SMR conditions because of H2 spillover from the surface of Ru onto the surface of Ni. Consequently, the addition of a small quantity of Ru to the Ni catalyst can improve the catalytic activity and stability during the DSS operation.

Preparation of Eggshell-Type Ru/Al2O3 Catalysts for Hydrogen Production Using Steam-Methane Reforming on PEMFC

Ru-based eggshell-type catalysts, in which Ru is located at the outer region of the pellet, were prepared by the impregnation method, using spherically shaped γ-Al2O3 pellets for steam-methane reforming (SMR). Ru was only supported on the external region of the pellet because of the strong interaction between its precursor and the alumina pellet. The Ru precursor penetrated the inside of the pellet by adding nitric acid to the impregnation solution. The distribution and thickness of the Ru layer in the catalyst can be controlled using the HNO3/Ru molar ratio and contact time at the impregnation step. Among the catalysts, the graded eggshell-type catalyst showed the highest activity and long-term stability in the SMR reaction. In addition, in the daily startup and shutdown (DSS) operation, similar to the hydrogen production environment for domestic polymer electrolyte membrane fuel cells (PEMFC), the graded eggshell-type catalyst showed high activity and stability after multiple cycles. Based on the experimental studies, it was confirmed that Ru-based catalysts are suitable for steam-methane reforming for PEMFC.

A Short Review on Ni Based Catalysts and Related Engineering Issues for Methane Steam Reforming

Hydrogen is an important raw material in chemical industries, and the steam reforming of light hydrocarbons (such as methane) is the most used process for its production. In this process, the use of a catalyst is mandatory and, if compared to precious metal-based catalysts, Ni-based catalysts assure an acceptable high activity and a lower cost. The aim of a distributed hydrogen production, for example, through an on-site type hydrogen station, is only reachable if a novel reforming system is developed, with some unique properties that are not present in the large-scale reforming system. These properties include, among the others, (i) daily startup and shutdown (DSS) operation ability, (ii) rapid response to load fluctuation, (iii) compactness of device, and (iv) excellent thermal exchange. In this sense, the catalyst has an important role. There is vast amount of information in the literature regarding the performance of catalysts in methane steam reforming. In this short review, an overview on the most recent advances in Ni based catalysts for methane steam reforming is given, also regarding the use of innovative structured catalysts.

Experimental performance evaluation of an ammonia-fuelled microchannel reformer for hydrogen generation

Microchannel reactors appear attractive as integral parts of fuel processors to generate hydrogen (H2) for portable and distributed fuel cell applications. The work described in this paper evaluates, characterizes, and demonstrates miniaturized H2 production in a stand-alone ammonia-fuelled microchannel reformer. The performance of the microchannel reformer is investigated as a function of reaction temperature (450–700 °C) and gas-hourly-space-velocity (6520–32,600 Nml gcat−1 h−1). The reformer operated in a daily start-up and shut-down (DSS)-like mode for a total 750 h comprising of 125 cycles, all to mimic frequent intermittent operation envisaged for fuel cell systems. The reformer exhibited remarkable operation demonstrating 98.7% NH3 conversion at 32,600 Nml gcat−1 h−1 and 700 °C to generate an estimated fuel cell power output of 5.7 We and power density of 16 kWe L−1 (based on effective reactor volume). At the same time, reformer operation yielded low pressure drop (<10 Pa mm−1) for all conditions considered. Overall, the microchannel reformer performed sufficiently exceptional to warrant serious consideration in supplying H2 to fuel cell systems.

Dimethyl ether steam reforming under daily start-up and shut-down (DSS)-like operation over CuFe 2O 4 spinel and alumina composite catalysts

The durability of the CuFe 2O 4 spinel and γ-Al 2O 3 composite catalysts for steam reforming of dimethyl ether (DME) was evaluated at 375 °C for 120 h under the daily start-up and shut-down (DSS) operation. No degradation could be observed for the catalyst subjected to the cooling–heating process in O 2 atmosphere. On the other hand, the catalyst performance was significantly degraded by the cooling–heating process in steam atmosphere due to the deactivation of the acid sites on γ-Al 2O 3 for DME hydrolysis reaction, leading to the loss of DME steam reforming activity. The higher amount of coke formation was also observed over the catalysts exposed to steam during the cooling–heating process, as compared with the catalysts exposed to O 2 or without DSS operation. The degraded catalyst could be recovered by the heat treatment in air at 375 °C, since the active sites of γ-Al 2O 3 were regenerated and the coke deposits were removed. Interestingly, the catalytic activity of the regenerated catalysts for methanol steam reforming was higher than the fresh one because of an increase in the metal surface area of Cu species after the regeneration treatment.

Steam reforming reactions over a metal-monolithic anodic alumina-supported Ni catalyst with trace amounts of noble metal

A trace amount of noble metal (Ru or Pt <0.1 wt%) was doped onto an anodic alumina-supported Ni catalyst, to investigate its performance in the steam reforming of methane (SRM), especially during DSS (daily startup and shutdown) operation. Although the steam purge treatment at high temperatures seriously deactivated the Ni catalyst because of the oxidation of metallic nickel with steam into Ni 2+, trace Ru assisted the regeneration of active metallic nickel by hydrogen-spillover. And, the Ni sintering was largely alleviated by the addition of Ru, and it was probably due to the formation of Ru–Ni alloy. In comparison with the Ru-doped Ni catalyst, the Pt-doped Ni catalyst showed a more favorable tolerance to steam oxidation, even at 900 °C. In a stationary SRM test of 3000 h and a DSS SRM test of 500 times where the town gas 13A was used as hydrogen source, no obvious deterioration was detected over the Pt-doped Ni catalyst. Especially, when electrically heating the plate-type Pt-doped Ni catalyst to 700 °C, the SRM reaction system could reach a stable state within ca. 10 min, which offered a strong possibility to shorten the startup time from the 1–2 h of conventional reformer to just few minutes. In addition, the noble metal-doped Ni catalyst also showed favorable activity and durability when being applied to other steam reforming systems, such as kerosene and ethanol.

Effect of Ru and Pt Addition over Plate-type Catalysts for Methane Steam Reforming during Daily Start-up and Shut-down

Abstract A plate-type anodic-alumina-supported 17.9 wt % Ni catalyst quickly deactivated in daily start-up and shut-down (DSS) steam reforming of methane at 700 °C. When 0.05 wt % Ru or Pt was doped, the catalyst exhibited self-activation, self-regeneration, and self-redispersion. The Pt–Ni catalyst showed better stability than Ru–Ni. A wave-shape Pt–Ni catalyst was prepared, while 3000 h continual and 500-time DSS stability was achieved. Nevertheless, for industrial application, some effort should be made to suppress the catalyst sintering.

Novel catalytic behavior of Cu/Al 2O 3 catalyst against daily start-up and shut-down (DSS)-like operation in the water gas shift reaction

Cu/Al 2O 3 catalysts (Cu/Al = 1/2) have been prepared by coprecipitation (CP-), homogeneous precipitation (HP-), sol–gel (SG-), and impregnation (IMP-) methods. Prepared Cu/Al 2O 3 catalysts were applied to the water gas shift (WGS) reaction. Effects of preparation method and calcination temperature on their activities for the WGS reaction and sustainability against the daily start-up and shut-down (DSS)-like operation between 323 and 473 K under steam treatment were investigated. CP-, HP-, and SG-Cu/Al 2O 3 catalysts showed a sustainable activity during DSS-like operation in the WGS reaction, whereas IMP-Cu/Al 2O 3 showed a quite low sustainability. CP-Cu/Al 2O 3 catalyst calcined at 823 K (CP-823) showed the highest activity and sustainability among the catalysts tested and almost similar to a commercial Cu/ZnO/Al 2O 3 catalyst (MDC-7) even after 50 cycles of the DSS-like operation in the WGS reaction. In contrast, CP-Cu/Al 2O 3 catalyst calcined at 1073 K (CP-1073) showed a low sustainability, although the initial activity was higher than that of CP-823. It was concluded that such prominent performances of the CP-823 catalyst is caused by (1) the formation of highly dispersed and stable Cu metal and (2) an important role of boehmite (AlO(OH)) phase formed during the DSS operation in inhibition of aggregation of Cu metal particles. For CP-1073, “ in-situ” formation of boehmite phase did not proceed due to the formation of stable CuAl 2O 4 phase by calcination at high temperature. Therefore, the activity of CP-1073 remarkably decreased as a result of aggregation of Cu metal particles during the DSS-like operation.

Hydrogen production by autothermal reforming of kerosene over MgAlO x-supported Rh catalysts

Autothermal reforming (ATR) of kerosene for hydrogen production was performed on the MgAlO x -supported Rh catalysts at LHSV of 15–25, S/C of 2.5, O/C of 0.5, at 101 kPa. Sphere-shaped supports with high compressive ultimate strength (0.90 MPa) were obtained from MG-30 hydrotalcite core (∼3 mm) by thorough heat treatment before impregnation of rhodium. Rhodium was loaded by pore-filling impregnation selectively to the surface of the sphere-shaped supports, confirmed by electron probe microanalysis. Stability tests on the prepared catalysts were performed, focusing on the small amount of C 2–C 3 hydrocarbons, concentrations of which reflect the catalytic activity and stability; i.e., low rates of C 2–C 3 olefin formation correspond to high activity of the catalysts. The reactor was designed to measure temperature profiles and gas distributions within the reactor (inner diameter ∼21.0 mm) and the catalyst bed (length 100 mm). The ATR reactions occur starting with an exothermic combustion of hydrocarbons, followed by an endothermic reforming. The maximum temperature reached ∼1200 K at the inlet of the catalyst bed and decreased to ∼1020 K towards the end of the catalyst bed. Among investigated catalysts, the catalysts treated in air at 1223 K gave the best performance for ATR of kerosene, giving H 2 production reaching 60% of the exit gas. The concentration of the main byproduct, C 2H 4, over the optimized catalyst was lower than 0.03% at the exit of the reactor for 50 h of the study. The catalyst showed high tolerance to coking and high stability even at LHSV of 25 and daily start-up and shut-down (DSS) cycles, meeting practical requirements for the ATR catalysts.

Citrate or hydrotalcite?

Trace amounts of Pt- and Ru-doped Ni/Mg(Al)O catalysts were prepared by a citrate method and tested in the oxidative reforming of C 3 H 8 under daily start-up and shut-down (DSS) operation. The activity and the sustainability of the catalysts were compared with those of the Pt- and Ru-doped Ni/Mg(Al)O catalysts derived from hydrotalcite (HT) precursor. The DSS operation of C 3 H 8 reforming was carried out with O 2 gas or O 2 /H 2 O mixed gas between 200 °C and 600 °C or 700 °C under air purging conditions. The catalysts underwent steaming treatment with H 2 /H 2 O mixed gas at 900 °C for 10 h. This allowed us to test the effect of Ni sintering on the catalyst deactivation. Coking was significantly suppressed on both HT- and citrate-derived Ni catalysts. Although both preparations produced highly dispersed Ni particles on the catalysts, the HT-derived catalysts exhibited more finely dispersed Ni particles, resulting in higher activity values than those of the citrate-derived catalysts. The regenerative activity due to redispersion of sintered Ni particles was enhanced over the HT-derived catalysts compared with the activity over citrate-derived catalysts. Although a clear redispersion of Ni particles was not observed in the oxidative reforming, i.e., in the absence of steam, the size decrease in Ni particles was more significant over the HT-derived catalysts than over the citrate-derived catalysts. The Mg(Al)O periclase structure derived from Mg-Al HT likely plays an important role in the regenerative activity of Pt- and Ru-Ni/Mg(Al)O catalysts. Pt-doping was more effective than Ru for the catalyst sustainability in the oxidative reforming of C 3 H 8 . Trace amounts of Pt-doped Ni/Mg(Al)O catalysts derived from hydrotaclite exhibited higher and more sustainable activity than those prepared by the citrate method. Mg(Al)O periclase that originated from Mg-Al HT played an important role in the regenerative activity of the catalysts via reversible reduction-oxidation between Ni 0 and Ni 2+ on/in Mg(Al)O assisted by hydrogen spillover from Pt.

High sustainability of Cu–Al–Ox catalysts against daily start-up and shut-down (DSS)-like operation in the water–gas shift reaction

Abstract Coprecipitated-Cu–Al–Ox catalyst calcined at 823 K (CP-823) showed higher activity and sustainability than a commercial Cu/ZnO/Al 2 O 3 catalyst even after 50 cycles of the daily start-up and shut-down (DSS)-like operation in the water–gas shift reaction. The high, stable activity of CP-823 is caused by the formation of highly dispersed and stable Cu metal. A boehmite phase formed “ in situ ” during the DSS operation has an important role in inhibition of aggregation of Cu metal particles.

Sustainable Ru-doped Ni catalyst derived from hydrotalcite in propane reforming

Trace amount of Ru-doped Ni/Mg(Al)O catalyst was prepared from hydrotalcite precursor and was tested in the reforming of propane under daily start-up and shut-down (DSS) operation. Mg(Ni,Al)O periclase derived from the hydrotalcite was dispersed in an aqueous solution of Ru nitrate, followed by calcination and reduction. Finely dispersed Ni–Ru was supported on Mg(Al)O periclase particles. The activity as well as the sustainability in the propane reforming was compared with the commercial Al 2O 3-supported Ni and Ru catalysts. The DSS operations of partial oxidation, steam reforming and autothermal reforming were carried out under steam or air purging conditions. The Ru doping suppressed the surface oxidation of Ni particles on the Ni/Mg(Al)O catalyst, resulting in the high activity as well as the high sustainability in all reforming reactions except under steam–air combined purging. The deactivation was effectively suppressed by increasing either reaction temperature or Ru doping even under steam–air combined purging. Ni particles also suffered by sintering, but the sintered Ni particles were redispersed and the activity was sustained during DSS operations. Air-purged partial oxidation was the most effective for the redispersion of the sintered Ni particles. This likely indicates that the finely dispersed Ni particles were continuously regenerated by reversible reduction–oxidation between Ni 0 and Ni 2+ via Mg(Ni)Al periclase assisted by hydrogen spillover from Ru or NiRu alloy.

A Plate-Type Anodic Alumina Supported Nickel Catalyst for Methane Steam Reforming

An anodic alumina supported nickel catalyst (Ni/Al2O3/Alloy) was synthesized using a double impregnation method with a high temperature calcination in between, to investigate reactivity performance thereof during steam reforming of methane (SRM) reactions in continuous and daily start-up and shut-down (DSS)-like operations. The catalyst was structurally characterized using X-ray diffraction (XRD), BET and temperature programmed reduction (TPR) technologies. The TPR results showed that almost all nickel content from the first impregnation was transformed into nickel aluminate, whereas nickel from the second impregnation predominantly existed in the more reducible forms of NiO and xNiO·Al2O3 (x < 1). The existence of these NiO and NiAl2O4 phases was identified by XRD.The catalyst provided high and stable SRM reactivity near the equilibrium value, while no deactivation was observed in continuous durability testing for 200 h at 800°C and 130 h at 700°C, and in DSS-like mode operation at 700°C. The investigation of the influence of methane and/or steam treatments on the reactivity of Ni/Al2O3/Alloy showed the catalyst is not disturbed by the methane treatment, whereas it is remarkably deactivated by the steam treatment. In addition, no differences in the reduction effect were found when using hydrogen or methane to regenerate a steamed catalyst.

Self-activation and self-regenerative activity of trace Rh-doped Ni/Mg(Al)O catalysts in steam reforming of methane

Ni/Mg(Al)O catalyst doped with trace amounts of Rh was tested in steam reforming of methane and the catalytic behavior was compared with the Ru-doped catalyst. Rh-doped Ni/Mg(Al)O catalyst showed a self-activation without any reduction treatment due to the ability for hydrogen production by CH bond cleavage. Such production led to the reduction of lattice Ni2+ in Mg(Al,Ni)O periclase to metallic Ni by hydrogen-spillover. The Rh-doped Ni/Mg(Al)O catalyst showed also a self-regenerative activity during a daily start-up and shut-down (DSS) operation of steam reforming of methane. NiRh alloy was formed in the surface layer of metallic Ni particles and Rh was located more profoundly in the particles than Ru in NiRu alloy on the Ru-doped catalyst. The Rh-doping exhibited a prominent performance, whilst the Ru-doping resulted in neither self-activation nor stable activity in the DSS operation. Although the catalyst deactivation took place by the Ni0 oxidation into the lattice Ni2+ in Mg(Al,Ni)O periclase, trace Rh assisted the regeneration of the active metallic Ni from the lattice Ni2+ by hydrogen-spillover. Even metallic Ni particles that had been strongly sintered on the Rh-Ni/Mg(Al)O catalyst by steaming at 900 °C were re-dispersed during the DSS operation, resulting in high and stable activity. The self-regeneration of the Rh-doped Ni/Mg(Al)O catalyst has been achieved by continuous rebirth of active Ni metal particles due to reversible reduction–oxidation between the metallic Ni on the surface and the lattice Ni2+ in Mg(Ni,Al)O periclase, i.e., oxidative incorporation of surface Ni0 into the lattice Ni2+ of Mg(Al,Ni)O and reductive migration of the lattice Ni2+ to the surface Ni0 by hydrogen-spillover.

Self-regenerative activity of Ni/Mg(Al)O catalysts with trace Ru during daily start-up and shut-down operation of CH 4 steam reforming

Ni/Mg(Al)O catalysts doped with trace Ru showed self-regenerative activity during a daily start-up and shut-down (DSS) operation of steam reforming of methane. Formation of Ru Ni alloy on the surface of fine Ni metal particles on the catalysts was strongly suggested by EXAFS and TPR measurements. The Ni/Mg(Al)O catalyst was passivated by the oxidative incorporation of Ni 0 to Ni 2+ in Mg(Ni,Al)O periclase, and trace Ru assisted the regeneration of Ni metal from the Ni 2+ by hydrogen spillover. Even notably sintered Ni metal particles on the Ni/Mg(Al)O catalyst by steaming were rapidly redispersed, resulting in the revelation of the high and stable activity during the DSS operation. The self-regeneration of the Ru Ni/Mg(Al)O catalysts can be achieved by the continuous rebirth of active Ni metal species assisted cooperatively by both Ni 2+ → Ni 0 reduction by hydrogen-spillover via trace Ru metal or Ru Ni alloy and reversible reduction–oxidation between Ni 0 and Ni 2+ in Mg(Ni,Al)O periclase.

Steam reforming of CH4 over Ni-Ru catalysts supported on Mg-Al mixed oxide

Ni0.5/Mg2.5(Al)O catalyst prepared from hydrotalcite precursors showed high and stable activity in the CH4 steam reforming, but was severely deactivated in the daily start-up and shut-down (DSS) operation under steam purging. The addition of Ru drastically improved the behavior of Ni0.5/Mg2.5(Al)O catalyst for the DSS operation. During the wet Ru loading on the Ni0.5/Mg2.5(Al)O catalyst, the reconstitution of hydrotalcite took place by “memory effect,” resulting in the formation of Ru-Ni alloy as well as the strong interaction between Ru and Ni after the calcination followed by reduction. This provided the catalyst with high sustainability probably by suppressing the oxidation of Ni metal by steam by hydrogen spillover from Ru. Only 0.05 wt% of Ru loading was enough to effectively suppress the deactivation.

Promoting effect of Ru on Ni/Mg(Al)O catalysts in DSS-like operation of CH4 steam reforming

Effects of Ru addition on the activity and the sustainability of Ni/Mg(Al)O catalysts were investigated in the daily start-up and shut-down (DSS) operation of the steam reforming of CH4. Mg2.5(Ni0.5)–Al hydrotalcite was prepared by coprecipitation and calcined to form Mg2.5(Al,Ni0.5)O periclase. When the powders of the periclase were dipped in an aqueous solution of Ru(III) nitrate, the hydrotalcite was reconstituted on the surface of Mg2.5(Al,Ni0.5)O particles, resulting in the formation of highly dispersed Ru/Ni bimetal supported catalysts after the calcination, followed by the reduction. The addition of Ru on Ni caused a decrease in the reduction temperature of Ni and an increase in the amount of H2 uptake on the Ni over the catalyst. Formation of Ru–Ni alloy or strong interaction between Ru and Ni was also suggested. When Ru–Ni0.5/Mg2.5(Al)O catalysts were tested in the DSS-like operation under steam purging, the deactivation due to the oxidation of Ni metal by steam was effectively suppressed by hydrogen spillover. Moreover, only 0.05wt% of Ru loading was enough to effectively suppress the deactivation during the DSS-like operation.

Numerical Analysis of Thermal Behavior of Small Solid Oxide Fuel Cell Systems

Recently, small solid oxide fuel cell (SOFC) systems have been developed for various applications because of their high performance. In such small generation systems, quick and frequent start-stops are often required. However, it is generally considered that these start-stops with SOFC systems are not preferable because SOFC systems are operated at high temperature. Also, quantitative studies on the thermal behavior of small SOFC systems are limited. The purpose of this paper is to obtain insight into the possibility of using small SOFC systems with quick and frequent start-stops. A simple two-dimensional numerical model for 1kW-class SOFC systems was fabricated to study this problem. The model consists of a cylindrical SOFC stack, a prereformer on the stack, a heat exchanger for exhaust gas, and a thermal insulator that covers the stack and the prereformer. Using this model, first, the characteristics of the power generation efficiency were estimated under various operating conditions. In addition, the validity of the modeling was verified. Next, the start-up dependence on their structure and operating conditions was investigated. Finally, for the cyclic daily start-up and shutdown (DSS) procedure, the total efficiency during a day was calculated when the energy loss during start-stops is considered. As a result of the analysis, the following points were found. First, the validity and accuracy of the modeling was established, and their efficiency under the rated condition becomes 60% (DC/HHV) at a steam-carbon ratio=2.5 and an oxygen utilization=50%. Next, the thickness of the thermal insulator (0.03W∕m∕K) is required to be more than 6cm to reduce the heat loss from the outer surface of the thermal insulator to &lt;5% of the provided fuel energy (2kW) under the rated condition. In this case, it takes ca. 150min to start, if the fuel (methane) flow rate is 3.02NL∕min, which is equivalent to 2kW of heat flow. Finally, for the DSS operation, consisting of repetition of a 16h operation and an 8h stop in a day, the total efficiency decreases by ca. 1.5% from the rated power generation efficiency. Therefore, it is clarified that 1kW-class SOFC systems can be quite suitable even in the case where quick and frequent start-stops are required.

Promoting effect of Rh, Pd and Pt noble metals to the Ni/Mg(Al)O catalysts for the DSS-like operation in CH 4 steam reforming

Effects of the additions of noble metal, i.e. Rh, Pd and Pt, on Ni/Mg(Al)O catalyst have been investigated for the daily start-up and shut-down (DSS) operation under steam purging in the steam reforming of CH 4. Mg 2.5(Ni 0.5)-Al hydrotalcite was prepared by coprecipitation and calcined to form Mg 2.5(Al,Ni 0.5)O periclase. When the powders of the periclase were dipped in an aqueous solution of the nitrate of Rh(III), Pd(II) or Pt(II), the hydrotaclite was reconstituted on the surface of Mg 2.5(Al,Ni 0.5)O particles due to a “memory effect,” resulting in the formation of highly dispersed noble metal-Ni supported catalysts after the calcination followed by the reduction. The addition of noble metal on Ni resulted in a decrease in the reduction temperature of Ni 2+ in Mg 2.5(Al,Ni 0.5)O periclase and an increase in the amount of H 2 uptake on the Ni 0 over the Ni/Mg 2.5(Al)O catalyst. When Rh-, Pd- and Pt-Ni 0.5/Mg 2.5(Al)O catalysts were tested for the DSS-like operation under steam purging, the deactivation due to the Ni metal oxidation by steam was effectively suppressed by hydrogen spillover from noble metal to Ni. Especially, only 0.05 wt% of noble metal loading was enough to suppress effectively the deactivation during the DSS-like operation in the case of using both Rh and Pt.

Sustainability of Ni loaded Mg–Al mixed oxide catalyst in daily startup and shutdown operations of CH 4 steam reforming

Daily startup and shutdown (DSS) operations using several purge gases were applied for Ni-loaded Mg(Al)O periclase catalyst to test the sustainability in steam reforming of CH 4. Thirteen wt% Ni loaded Mg(Al)O catalysts were prepared by using Mg(Ni)–Al hydrotalcite as the precursor with varying Mg/Al ratios. H 2O/N 2 (100/25 ml min −1), O 2/N 2 (40/10 ml min −1) and CO 2/H 2O/N 2 (40/15/25 ml min −1) were tested as the purge gas in imitation of steam, air and spent gas, respectively. Use of air as the purge gas resulted in a quick deactivation of all Ni loaded catalysts due to the oxidation of Ni metal on the catalyst surface. Spent gas was the most inert for the DSS operation causing no significant deactivation of Ni loaded catalysts. Steam, the most convenient purge gas for DSS operation of PEFC, revealed evident deactivation depending on the (Mg + Ni)/Al ratio in Ni/Mg(Al)O catalysts; use of the (Mg + Ni)/Al ratio of 3/1 resulted in a quick deactivation with steam purge, although this ratio was the most profitable for the steady state operation with the Ni/Mg(Al)O catalysts. The most stable operation was achieved with the ratio of 6/1 in steam as the purge gas. The deactivation took place mainly by the oxidation of Ni metal by steam as the purge gas during the DSS operation between 200 and 700 °C. It is likely that Mg(Al)O on the Ni/Mg(Al)O catalysts was hydrated by steam to form Mg(OH) 2 on the catalyst surface, resulting in the oxidation of Ni metal finely dispersed on Mg(Al)O periclase.