Tuning reactivity of Fischer–Tropsch synthesis by regulating TiOx overlayer over Ru/TiO2 nanocatalysts

The activity of Fischer–Tropsch synthesis (FTS) on metal-based nanocatalysts can be greatly promoted by the support of reducible oxides, while the role of support remains elusive. Herein, by varying the reduction condition to regulate the TiOx overlayer on Ru nanocatalysts, the reactivity of Ru/TiO2 nanocatalysts can be differentially modulated. The activity in FTS shows a volcano-like trend with increasing reduction temperature from 200 to 600 °C. Such a variation of activity is characterized to be related to the activation of CO on the TiOx overlayer at Ru/TiO2 interfaces. Further theoretical calculations suggest that the formation of reduced TiOx occurs facilely on the Ru surface, and it involves in the catalytic mechanism of FTS to facilitate the CO bond cleavage kinetically. This study provides a deep insight on the mechanism of TiOx overlayer in FTS, and offers an effective approach to tuning catalytic reactivity of metal nanocatalysts on reducible oxides.

m 2 g -1 ) can be calculated by the integration of the peak area corresponding to upd 66 stripping. In this process, we assume that a single Cu atom deposits on one surface Ru 67 to form a monolayer deposition, which can be realized by judicious choice of 68 electrochemical potential and deposition time.  (2) 82 where the numerator was determined from the Cu upd data and ω Ru , the mass fraction 83 of Ru, was determined by ICP-OES. 84 The dispersion of the metallic Ru, D, was determined by the equation where M Ru is the atomic mass of Ru (101.07 g mol -1 ), N A is Avogadro's number (6.02 87 × 10 23 mol -1 ) and a m is the area occupied by a surface atom (for Ru, a m = 6.35 Å 2 ). selectivity can be determined by the peak areas of the components identified by TCD.

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The CO conversion, X CO , was calculated using the equation where n in (CO) and n out (CO) refer to the mole number of CO at the inlet and outlet, 108 respectively, A in (CO) and A in (Ar) refer to the chromatographic peak area of CO and Ar 109 in the feed gas, and A out (CO) and A out (Ar) refer to the chromatographic peak area of 110 CO and Ar in the off-gas.

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The reaction rate was calculated as where GHSV is the gas hourly space velocity and ω Ru is the mass fraction of Ru (2.2 114 wt% detected by ICP-OES).

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The turnover frequency (TOF) was determined using the equation where M Ru is the atomic mass of Ru (101.07 g mol -1 ) and the Ru dispersion was 7 determined by the CO chemisorption results.

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The selectivity values presented in this work were calculated on a carbon basis.

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The selectivity of CO 2 was calculated as 122 where f CO2/Ar is the relative correction factors of CO 2 to Ar, which was determined by 123 the calibrating gas; A out (CO 2 ) refers to the chromatographic peak area of CO 2 detected 124 by TCD in the off-gas.

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Similarly, the selectivity of CH 4 was calculated as where f CH4/Ar is the relative correction factors of CH 4 to Ar, which was determined by 128 the calibrating gas; A out (CH 4 ) refers to the chromatographic peak area of CH 4 detected 129 by TCD in the off-gas.

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The flame ionization detector (FID) were used to detect CH 4 and C 2 -C 4 131 hydrocarbons. The CH 4 selectivity was used as a bridge to calculate the selectivity of 132 C 2 -C 4 hydrocarbons identified by FID.

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The selectivity for C x H y (x = 2-4) hydrocarbons was calculated as Here, the chemical potential of O atom (μ o ) is restrained between      suggests that the size of Ru can keep constant after testing (Supplementary Figure 15).

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This was also benefited from the SMSI in the Ru/TiO 2 -450 catalyst, which greatly 385 prohibits the size aggregation of Ru during FTS process.