High temperature WGS catalysts

Today s low- and high-temperature WGS catalysts are sufficiently active and stable for use in stationary facilities for 2-10 years before requiring replacement. The incentive for companies to develop catalysts that last longer than 10 years is limited. Even so, it is reasonable to expect some advance to occur within the next several years just as it did when Cu was added to the iron-chromia high-temperature catalysts about 20 years ago. 

Kumar and Idem [43] synthesized Cu/Ni/Ce02-Zr02 and compared with commercial low- and high-temperature WGS catalysts. Under the reformate conditions, Cu/Ni/Ce02-Zr02 was found to be more stable with no apparent activity loss compared to both commercial low- and high-temperamre WGS catalysts. They proposed that the superior catalytic performance of... 

TABLE 93 Reaction Orders and Activation Energies of Various High-Temperature WGS Catalysts... 

High- and low-temperature WGS catalysts based on Fe and Cu respectively, require slow and carefully controlled activation procedures. After reduction they are highly reactive toward air and can be a fire hazard to the consumer. 

While both base metal and precious metal catalyst formulations performed well in a simulated high temperature WGS feed stream (-15% CO), precious metal catalysts were clearly superior when tested with a low temperature WGS feed stream (-5% CO). Results for a Siid-Chemie copper zinc catalyst (T2650) and a Siid-Chemie precious metal-ceria catalyst (PMS5) are shown in Figure 5, tested in a simulated low temperature WGS feed stream. Equilibrium was achieved for the PMS5 catalyst for... 

Lee et al. [30] replaced Cr with Ni, Zn, Co doped in the iron oxide. Performance of the catalysts in high-temperature WGS reaction was evaluated under gas mixture conditions (42% H2, 10% CO, 37% H2O, 8% CO2 and 3% CH4). Among the prepared catalysts, Zn5FeNi20 and Co5FeNi20 catalysts showed good catalytic activity (around 65-75% CO conversion at 400 °C) in the HTS condition of LPG reformate. 

Li et al. [34] synthesized Fe-Al-Ce catalysts and compared with Fe-Cr catalysts and evaluated for high-temperature WGS reaction under simulated coal derived syngas at a steam to CO ratio of 1. The Fe-Al-Ce catalyst exhibits better activity compared to Fe-Cr catalyst. 

Meshkani Rezaei [39] synthesized mesoporous Ba promoted Fe-Al-Ni catalysts for the high-temperature WGS reaction. Fe-Al-Ni and Fe-Al-Ni-Ba catalysts exhibit better catalytic activity than commercial catalysts. Also Ba addition suppresses the methanation activity. 

In 2004 Qi and Stephanopoulos [40] reported Cu-Ce02 catalysts for the high-temperature WGS reaction. They also investigated the effect of La addition in the Ce lattice on the WGS activity. The catalytic results of various Cu-Ce02-La203 catalysts, Fe-Ce catalysts, pure Ce-La and commercial catalyst are presented in Figure 2.7. As expected, pure Ce-La catalyst exhibits lower conversion compared to remaining catalysts. The Fe-Ce(8% samples have... 

Reports are also available on investigation of metal sulphides other than Co-Mo for the WGS reaction. Valsamakis and Stephanopoulos [26] investigated La and Pr sulphided for high temperature WGS reaction. They prepared catalysts... 

Fe is the active metal for high-temperature WGS reaction. Hence, we introduced a variety of metal dopants (M = Cr, Mn, Co, Ni, Cu, Zn and Ce) for iron oxide (spinel lattice) and screened their effectiveness for high-temperature WGS reaction [1]. The idea was to examine if ferrite formation can occur with dopants and promote the Fe Fe redox couple. The substitution of Fe sites in the ferrite strucmre with other transition/non-transition/inner transition metal atoms leads to the crystallization of an inverse (or mixed) spinel. The stoichiometry of an inverse spinel can be represented as A(i a)Ba[AaB(2 a)]04, where 8 is the degree of inversion, while A and B represent typical divalent and trivalent cations, respectively. The catalysts were synthesized by coprecipitation method using nitrates as precursors. The synthesized catalysts were evaluated for ultra high temperature WGS reaction in the temperature region 400-550 °C and GHSV 60,000 h- ... 

Then we incorporated Cu into the Fe/M catalysts (M = Cr, Mn, Co, Ni, Cu, Zn and Ce) since Cu is a promoter for the Fe/Cr catalysts for the high-temperature WGS reaction in the industries [3-5]. Interestingly, Cu acts as a promoter for all the modified ferrite catalysts except Fe/Ce catalyst. It acts as an inhibitor for the Fe/Ce catalyst. These results show that all of the copper co-doped ferrites behave like Fe/Cr/Cu except Fe/Ce/Cu, which behaves differently for high-temperature WGS reaction. We explained this interesting behaviour of copper... 

G. K. Reddy, P. Boolchand, P. Smimiotis, Sulfur tolerant metal doped Fe/Ce catalysts for high temperature WGS reaction at low steam to CO ratios - XPS and Mossbauer spectroscopic study, J. Catal. 282 (2011) 258-269. 

To achieve the complete CO conversion, the WGS reaction after coal gasification is conducted in two adiabatic reactors, i.e., high temperature WGS reactor (310—450 °C) and low temperature WGS reactor (200—250 °C). The two reactors are arranged in series so the raw syngas flowing out of coal gasifier enters the high-temperature WGS reactor packed with Fe-based catalyst first, followed by the low-temperature WGS reactor packed with Cu-based catalyst (Man et al., 2011). 

The use of these catalysts presents some drawbacks such as slow kinetics or the pyrophoric nature of the Cu—Zn0/Al203, which can hinder the application in small devices like fuel cells attached to small-scale gasifiers. Different alternatives to the conventional catalysts have been proposed, including Co-V binary oxides and noble metals supported in Ce02 for low-temperature WGS, and Co—Mo and Ni—Mo sulfides for high-temperature WGS (Navarro et al., 2007 Huber et al., 2006 Gonzalez Castano et al., 2014 Reina et al., 2014, 2015). 

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