Fischer–Tropsch synthesis on the Al2O3-modified ordered mesoporous Co3O4 with an enhanced catalytic activity and stability

Ordered Mesoporous Co3O4−Al2O3 Binary Metal Oxides for CO Hydrogenation to Hydrocarbons: Synergy Effects of Phosphorus Modifier for an Enhanced Catalytic Activity and Stability

“…The binding energy (BE) of Co 2p 3/2 on the fresh P/m-CoAl was found to be in the range of 781.5-781.9 eV without significant variations as shown in Figure 2(B-1) and Table 2. This observation indicates that the outmost surfaces of the P/m-CoAl were mainly composed of the spinel-type Co 3 O 4 phase by observing a slightly higher BE than the monometallic Co 3 O 4 phase, [46] which was originated from the stronger interaction between the Co 3 O 4 and Al 2 O 3 (or AlPO 4 ). The satellite peak appeared at~788 eV on the fresh P/ m-CoAl corresponding to a shake-up process of a higher spin of Co n + species [50] can be possibly attributed to the strongly interacted Co 3 O 4 nanoparticles with Al 2 O 3 or spinel-type CoAl 2 O 4 [51] and Co 3 (PO 4 ) 2 .…”

“…higher CO conversions above 71 % were observed on the P(1)/ m-CoAl and P(3)/m-CoAl with a higher C 5 + selectivity above 69 % with a small CO conversion to CO 2 below 3.9 % (i. e., CO 2 yield below~3 %). In addition, those optimal P/m-CoAl catalysts also showed higher structural stabilities and catalytic activities than the phosphorous-free P(0)/m-CoAl [46] with CO conversion of 66.0 % and C 5 + selectivity of 64.9 %. The olefin selectivity in the range of C 2 -C 4 hydrocarbons was also maximized on the most active and stable P(3)/m-CoAl with that of 29.8 % compared to that of the P(0)/m-CoAl.…”

“…The first reduction peaks on the P/m-CoAl were slightly increased up to 383-389°C on the phosphorous-modified m-CoAl from 374°C on the P(0)/m-CoAl, which can be assigned to the reduction of Co 3 O 4 !CoO or partial reduction of surface cobalt oxides by forming the strongly interacted cobalt crystallites possibly. [10][11][12][13][14][15][16][17]46] A slight shift to lower temperatures of the first peaks on the phosphorous-modified m-CoAl with an increase of phosphorous content from 389°C on the P(1)/m-CoAl to 383°C on the P(10)/m-CoAl was originated from the weakened interactions of the Co 3 O 4 on the hydrophobic SiO 2like AlPO 4 surfaces than that of acidic Al 2 O 3 . [47] This can be possibly related with a less thermal stability of Co 3 O 4 nanoparticles at a higher phosphorus content on the Al 2 O 3 by forming the much larger cobalt aggregates or structural disintegrations of the ordered mesoporous Co 3 O 4 À Al 2 O 3 frameworks.…”

“…Interestingly, the amount of the thermally stable and irreducible spinel-type CoAl 2 O 4 phases was also increased with an increase of phosphorous content from 0.9 % on the P(0)/m-CoAl to 0.6-4.6 % on the phosphorous-modified m-CoAl. It seems to be attributed to the possible phase transformations from metal phosphates such as Co 3 (PO 4 ) 2 and AlPO 4 to the thermally stable spinel-type CoAl 2 O 4 phases, [10][11][12][13][14][15][16][17]46,48] which can be originated from the much stronger affinity between phosphorous and aluminum species than that of cobalt species. [19][20][21][22][23][24] The white line area (WL) on the fresh P/m-CoAl as summarized in Table 1 also showed very similar values in the range of 2.24-2.47, which can be also related with the oxidation states of cobalt nanoparticles.…”

“…This odd observation on the P(5)/m-CoAl with the initially highest activity (CO conversion of 93.5 %) and fast deactivation from an early reaction stage can be attributed to complete structural collapses during FTS reaction, [5,62] which was due to the hot-spots formed by a highly exothermic FTS reaction to accelerate the formation of Co(PO 4 ) 2 · xH 2 O phase. Therefore, the observed lowest CO conversion of 25.4 % (TOF of 0.078) and highest initial CO 2 production rate (CO conversion to CO 2 of 35.1 %) on the P(10)/m-CoAl were mainly caused by an excess formation of inactive cobalt phosphates by prohibiting CO adsorption capacity and by increasing the structural instability as well, [13,19,20,23,46,48] which also increased water-gas shift (WGS) reaction activity on the metal oxides. [13(b)] On the most active and stable P(1)/m-CoAl and P(3)/m-CoAl, a chaingrowth probability (α), plotted by Anderson-Schulz-Flory (ASF) distribution in the range of C 5 -C 30 hydrocarbons, and product distribution with time on stream (supplementary Figure S10 for non-linear distributions of C 1 -C 3 due to multiple and secondary reactions of olefins formed [63,64] ) were found to be slightly larger in the range of 0.804-0.824 (Table S2) than those of the less active P(0)/m-CoAl and P(5)/m-CoAl with the values of 0.790-0.797.…”