Stabilized ordered-mesoporous Co3O4 structures using Al pillar for the superior CO hydrogenation activity to hydrocarbons

Adjusting Hydrocarbon Distribution on the Stabilized Al‐Modified Mesoporous Co3O4‐Fe2O3 Bimetal Oxides for CO Hydrogenation

“…[24] These phenomena were supported by the observed much larger surface areas on the Al-unmodified m-CoFe-u with the values of 55.3-73.1 m 2 /g and their smaller pore diameters in the range of 7.4-12.7 nm as summarized in supplementary Table S1. [38] According to our previous works on a highly ordered mesoporous monometallic Co 3 O 4 , [25][26][27][28][29] two separate reduction peaks appeared at~370 and 446°C can be assigned to the successive two step reductions (Co 3 O 4 + H 2 !3CoO + H 2 O and 3CoO + 3H 2 !3Co + 3H 2 O), and the middle reduction peak at 402°C can be assigned to the partially aggregated cobalt nanoparticles with its much higher reduction peak at 724°C possibly assigned to the spinel-type CoAl 2 O 4 [25,28,35] In case of the Fe-based metal oxides, hematite Fe 2 O 3 phases can be generally known to be reduced through three step reductions such as α-Fe 2 O 3 !Fe 3 O 4 !FeO!Fe 0 . [39] Those characteristic TPR peaks on the ordered mesoporous m-CoFe bimetal oxides shifted to the much higher temperatures, and the maximum temperature peaks of 656 and 758°C can be separately assigned to the reduction behaviors of Fe 2 O 3 and CoFe 2 O 4 phases to metal nanoparticles.…”

“…The Al 2 O 3 promoter can also partially generate the thermally stable spinel-type CoAl 2 O 4 , which possibly acted as a structural stabilizer of the highly ordered mesoporous structures as reported by our previous works through X-ray absorption fine structure (XAFS) analysis. [34][35][36] The presence of the spinel-type CoAl 2 O 4 phases was verified through various characterization tools, [25,34] Specific surface area (S g , m 2 /g), pore volume (P V , cm 3 /g) and average pore diameter (P D , nm) of the fresh m-CoFe are summarized in Table 1. Similar with the N 2 sorption patterns of the pristine KIT-6 (S g = 764 m 2 /g and P D = 5.2 nm) as shown in supplementary Figure S1, N 2 adsorption-desorption patterns (supplementary Figure S2(A)) and their pore size distributions (supplementary Figure S2(B)) on the fresh m-CoFe revealed the characteristic type IV isotherm with H1 hysteresis pattern.…”

“…These observations are the general trends of the ordered mesoporous metal oxides synthesis by using the hard templating methods due to an incomplete replica efficiency. [20,[24][25][26][27][28]37,38] Especially, the less ordered mesoporous structures on the m-CoFe bimetal oxides can be also attributed to the partial structural disintegrations as well, which caused the much smaller specific surface area and larger average pore diameter on the bimetal oxides derived from the KIT-6 template. [28] We believe that an excessive amount of metal precursors on the outer surfaces of the KIT-6 mesopores can preferentially induce non-porous segregated bulk Co or Fe oxides, which can enhance the disintegrations of the ordered mesoporous structures on the bimetal m-CoFe.…”

“…Interestingly, the BEs of Co 2p and Fe 2p on the used m-CoFe (0.5) and m-CoFe(1) were slightly shifted to the higher BEs after FTS reaction from~780 to > 781 eV and 710 to > 711 eV, respectively (Table S2) Those hardly reducible and thermally stable Co 3 O 4 -Fe 2 O 3 metal oxides were responsible for an enhanced structural stability as clearly reported from our previous works. [24][25][26][27][28]34] As summarized in Table 1 and supplementary Table S2, the surface atomic ratios and its oxidation states on the fresh and used m-CoFe based on deconvoluted patterns as shown in Figure 3 were significantly altered after FTS reaction for 60 h on stream. The oxidation states of Co species on the bimetallic m-CoFe (ratios of I Co3 + /I Co2 + assigned to the respective BEs of~780 eV and shoulder peak at~781 eV) were significantly decreased from 1.23-1.81 on the fresh m-CoFe to 0.57-0.74 on the used ones due to the reductive FTS reaction conditions, although the BEs were slightly increased on the used m-CoFe due to the formations of strongly interacted Co 3 O 4 -Fe 2 O 3 frameworks as confirmed by the previous results.…”

“…[23,24] To suppress the catalytic deactivations, which can be originated from the structural disintegrations of the ordered mesoporous transition metal oxides such as Co 3 O 4 or Fe 2 O 3 , the irreducible metal oxides such as Al 2 O 3 or ZrO 2 promoters can be mixed together to increase the structural stability by forming the thermally stable spinel-type metal oxide phases such as metal aluminates as reported by previous works. [25][26][27][28][29] For example, the irreducible Al 2 O 3 pillaring material in the highly ordered mesoporous Co 3 O 4 structures dramatically increased the structural stability as well as catalytic activity by forming the spinel-type CoÀ Al interfaces in the active metal matrices. However, the mutual roles of two reducible transition metal oxides such as the mesoporous Co and Fe oxide nanoparticles for FTS reaction have not been well investigated till now as far as we know with respect to their structural and catalytic stability with its larger amounts of light hydrocarbons without using any acidic zeolites.…”