Promoting the Selectivity of Pt/m-ZrO2 Ethanol Steam Reforming Catalysts with K and Rb Dopants

Abstract

The ethanol steam reforming reaction (ESR) was investigated on unpromoted and potassium- and rubidium-promoted monoclinic zirconia-supported platinum (Pt/m-ZrO2) catalysts. Evidence from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization indicates that ethanol dissociates to ethoxy species, which undergo oxidative dehydrogenation to acetate followed by acetate decomposition. The acetate decomposition pathway depends on catalyst composition. The decarboxylation pathway tends to produce higher overall hydrogen selectivity and is the most favored route at high alkali loading (2.55 wt.% K and higher or 4.25 wt.% Rb and higher). On the other hand, decarbonylation is a significant route for the undoped catalyst or when a low alkali loading (e.g., 0.85% K or 0.93% Rb) is used, thus lowering the overall H2 selectivity of the process. Results of in situ DRIFTS and the temperature-programmed reaction of ESR show that alkali doping promotes forward acetate decomposition while exposed metallic sites tend to facilitate decarbonylation. In previous work, 1.8 wt.% Na was found to hinder decarbonylation completely. Due to the fact that 1.8 wt.% Na is atomically equivalent to 3.1 wt.% K and 6.7 wt.% Rb, the results show that less K (2.55% K) or Rb (4.25% Rb) is needed to suppress decarbonylation; that is, more basic cations are more efficient promoters for improving the overall hydrogen selectivity of the ESR process.

The Route from Green H2 Production through Bioethanol Reforming to CO2 Catalytic Conversion: A Review

“…The addition of Cs to a zirconia support for a Pt/ZrO 2 catalyst was shown to improve the catalyst activity towards the ethanol decarboxylation route over the decarbonylation pathway, thus enhancing the hydrogen production rate [34]: a cesium loading of 2.9 wt% was able to stave off decarbonylation almost completely; under the same operating conditions (450 • C, 1 atm, and H 2 O/C 2 H 5 OH = 9), the amount of sodium that is required to achieve the same effect is almost 80% higher [35]. Similarly, the contribution of the latter route can be augmented by promoting monoclinic zirconia with 3.1 wt% K or 6.7 wt% Rb [36].…”

Tuning the Physicochemical Properties of Nanostructured Materials through Advanced Preparation Methods

“…In the field of catalysis, the preparation of the supported catalyst is, in many cases, crucial for the performance of the catalyst. The main physicochemical characteristics of the supported catalyst can be defined by the preparation route and the composition of the active phase [ 6 ]. For example, monoclinic zirconia-supported platinum (Pt/m-ZrO 2 ) catalysts are active for the ethanol steam-reforming reaction.…”

“…Thus, the overall hydrogen selectivity is significantly different between the two cases. Detailed studies with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and the temperature-programmed reaction of ethanol steam reforming show that alkali doping promotes forward acetate decomposition while exposed metallic sites tend to facilitate decarbonylation [ 6 ].…”