(105b) Ni-CaO-ZrO2 Nanocomposite Catalyst for CO2 Reforming of CH4 | AIChE

(105b) Ni-CaO-ZrO2 Nanocomposite Catalyst for CO2 Reforming of CH4


Zhao, T. - Presenter, Shanghai Advanced Research Institute, CAS
Zhang, J., Shanghai Advanced Research Institute, CAS
Sun, Y., Institute of Coal Chemistry, Chinese Academy of Sciences

  1. 1.       Introduction

Recently, utilization of natural gas to fuels and chemicals receives more attention due to its abundance over the world and less CO2 emission. The production of syngas by CO2 reforming of methane is one of the attractive routes to reach this goal. Compared with conventional steam reforming, CO2 reforming reaction tends to easier coking formation and needs extra 20% heat to obtain similar conversion. Nickel-based catalysts have shown an excellent behavior in this reaction with a comparable activity to noble metal catalysts [1]. However, coke formation  and sintering of nickel particles at a high temperature condition are often observed on Ni catalysts [2].  Developing a high-temperature stable catalyst is highly interesting for this reaction by controlled synthesis of catalyst. In this contribution, a stable Ni-CaO-ZrO2 nano-composite catalyst for CO2 reforming of CH4 is prepared by a coprecipitation method. The effect of preparation condition is carefully investigated. The relationships between catalyst structures and activity of nanocomposite catalysts are discussed.

  1. 2.       Experimental

Ni-CaO-ZrO2 catalysts were prepared by a coprecipitation method with a reflux-digestion process. After precipitation, the obtained slurry was washed and refluxed in de-ionized water, then filtered, dried and calcined at 600 oC for 5 h. The catalysts prepared at different reflux-digestion condition were assigned as NC-X-Y, where X and Y are the reflux temperature and time, respectively. The catalyst without reflux was assigned as NC-0. The reforming reaction was conducted at 850-900 °C in a quartz fixed-bed reactor at atmospheric pressure. Obtained catalysts are tested by feeding the reaction mixture of CO2 and CH4 (molar ratio 1.2: 1) without dilution and a gas hourly space velocity (GHSV) of 79 000 ml/(hg) . In addition, comparison of calciantion procedure and coking quantity was performed at different operating conditions.

  1. 3.       Results and discussion

3.1 Physical and chemical properties of the Ni-CaO-ZrO2 catalysts

The pore structure parameters are collected in Table 1. The catalyst without reflux-digestration has the smallest specific surface area (63 m2/g) and pore volume (0.09 cm3/g). With the increase of the reflux time, the specific surface area and pore volume of the catalysts increased. NC-100oC-24h exhibits the largest surface area of 245 m2/g. Reflux temperatures also have a significant effect on the pore structures of the catalysts. At the same reflux time, the specific surface areas of the catalysts increased with increasing the reflux temperature.

Table 1.  Pore structure parameters of the catalysts
























NC-60 oC-24h




NC-80 oC-24h




The XRD patterns of the catalysts prepared at different reflux-digestion condition are shown in Figure 1. The catalyst without reflux has strong diffusion peaks of ZrO2 and NiO. As the increase of the reflux time and temperature, diffusion peaks assigned to ZrO2 and NiO became weaker and wider. This result indicates that reflux digestion improves the dispersion of NiO and decreases the size of ZrO2 crystals in the catalysts.

TPR profiles of Ni-CaO-ZrO2 catalysts are illustrated in Figure 2. The peak or shoulder at about 400 oC is attributed to the reduction of large NiO particles, while the peaks at 600 oC and 700 oC may belong to the reduction of NiO that have the weak and strong interactions with ZrO2, respectively. For the catalyst without reflux, NiO mostly has the weak interaction with the carrier or is in the form of bulk particles. At the reflux temperature of 100 oC, the interaction between NiO and ZrO2 became stronger with the increase of reflux times (Figure 2 a). However, when the reflux temperature is lower than 100 oC, the interaction between NiO and carrier was not significantly enhanced (Figure 2 b). So the high reflux temperature and long reflux time are key factors to prepare the catalysts with strong interaction between metal and the carrier.

Figure 1.  XRD patterns of the catalysts     Figure 2. TPR profiles of the catalysts

3.2 Activity of the Ni-CaO-ZrO2 catalysts for CO2 reforming of methane

Results of the catalytic tests at 850 oC with a high GHSV (CO2/CH4=1.2:1) of 79, 000 ml/(h·g) are shown in Figure 3(a). The catalyst without reflux has a low activity with the CH4 conversion of about 70 %. In addition, CH4 conversion of this catalyst decreased with time and only 55% (conversion) is achieved after reaction on stream for 150 h. A higher conversion of CH4 and stability (very close to equilibrium) is observed on the catalyst refluxing at 100oC for 24 h. Therefore, prolonging the reflux time will increase activity of Ni-CaO-ZrO2 catalysts for CO2 reforming of methane. The catalyst with 24 h reflux-digestion (NC-100 oC-24h) exhibits a highly stable activity over 1000 h without obvious deactivation at a GHSV of 79, 000 ml/(hg) at850 oC (Data are not shown) .

NC100-24 h

Figure 3.  Catalytic performance of catalysts for CO2 reforming of methane

(a)     Effect of reflux temperature and time; (b) Effect of calcination temperature; (c) Effect of calcination procedure

Furthermore, the calcination temperature effect on the catalyst activity is carried out at similar operating conditions. It is found that the activity decreases when the sample is calcined at static air at a higher temperature. The NC-100-24h sample calcined at 900oC presents a very low activity (Fig.3b) . XRD examination indicates that monoclinic ZrO2 is gradually formed and particle size of ZrO2  becomes larger. TPR measurement indicates no obvious peaks for NiO reduction for the sample calcined at 900oC. These observations indicate that the sintering occurs at high temperatures. However, if the catalyst is directly reduced in the mixtures of H2 and N2 at 850oC or 900oC for 3 h, the conversion of CH4 still can maintain a high CH4 conversion (Fig. 3c),  implying that the calcination procedure has a profound impact on the activity of catalyst. Interestingly, the catalyst performing at 900oC gives a lower carbon deposition than 850 and 800oC after time on stream for 200 h. The full operating window will be given by a more systematic study afterwards.

  1. 4.       Conclusions

A high-temperature stable Ni-CaO-ZrO2catalyst is developed by the coprecipitation method with a reflux-digestion process. Reflux digestion can improve the dispersion of NiO and enhance the strong interaction between metal and support. The obtained Ni-CaO-ZrO2 catalyst can be further improved by modifying the calciantion procedure.


[1] J. R. Rostrup-Nielsen, J. H. B. Hansen, Journal of Catalysis 144 (1998).

[2] C. J.Liu, J. Y. He, J. J. Jiang, Y. X.Pan, ChemCatChem 3 (2011)