*2.6. CO Hydrogenation Performance*

Table 4 lists the catalytic performance of all the investigated catalysts. The carbon monoxide hydrogenation performance of the different molar ratio of Co/Ga for LaCoyGa1−yO3 catalyst were explored in our lab, and the results revealed the optimum molar ratio is 0.65/0.35 [30]. Therefore, the molar ratio of Co/Ga of all the investigated samples was fixed at 0.65/0.35.

**Figure 6.** TEM images (**a**–**c**), line scanning profiles, EDS mapping image (**d**), and the elements distribution of La (**e**), K (**f**), Co (**g**), and Ga (**h**) for LKCG-0.1 after 200 h stability tests.


Reaction conditions: P = 4 MPa, H2/CO/N2 = 8/4/1, T = 290 ◦C, GHSV = 6000 mL gcat−1·h−1. <sup>a</sup> Xco is CO conversion. <sup>b</sup> Sco2 is the selectivity to CO2. <sup>c</sup> SROH is the selectivity to the total alcohols. i in Ci is number of carbon atoms for the carbon-contained products. C4+ represents the carbon-contained products with 4 or more carbon atoms.

As for LCG, seen from the above TEM and XRPD results, the composition after reduction is the same with that after reaction, and all are Co/La4Ga2O9. In addition, the smaller BET surface area for LCG makes the Co nanoparticle severely sintered and unevenly dispersed (see in Table 2), thus resulting in a poor activity. At the same time, the larger Co particle sizes and the strong effects between Ga and La in the catalyst are also detrimental to the generation of the Co-Ga interfaces. The interfaces of Co and Ga were usually considered to be the active sites for HAS [16], while metal cobalt was the active sites of hydrocarbon generation [14]. Therefore, the LCG catalyst has the highest hydrocarbon selectivity among all the samples.

However, as for LKCG-0.1 catalyst, the main composition after reduction is Co/K2O-La2O3- LaGaO3 and the main composition after reaction is Co/K2O-La2O3-La2O2CO3-LaGaO3 (seen from the XRPD results). It is known from Table 4 that the catalyst with the optimal catalytic performance is LKCG-0.1. Since they have a larger specific surface area, cobalt nanoparticles are highly dispersed on the catalyst surface, which can be seen in Figure 5 and Table 2. In addition, since all the elements located in the lattice of perovskite, smaller size and uniformly dispersed cobalt nanoparticles are also conducive to generating more Co-Ga interfaces. In the process of reaction, cobalt exists in the form of Co0. The close contact of cobalt with the Co-Ga interface at the atomic level is beneficial to the synergistic effect of the catalyst, and thus the LKCG-0.1 catalyst exhibits the best catalytic performance. In addition, the electron donating effect of K can promote the increase of the selectivity of higher alcohols [31–34].

For the LKCG-0.2 catalyst, with the increasing of K content, the catalytic activity decreased, for that the addition of K can make part of Co outside the perovskite structure, resulting in a non-uniform dispersion of Co and Ga. A relatively lower activity and selectivity is observed in Table 4.

Other catalysts with outstanding performance reported in the literature are revealed in Table 5 [17,35–38]. By comparison, the activity of LKCG-0.1 catalyst in this work is not the optimal, but it may be one of the good catalysts in general considering relatively lower reaction temperatures and higher alcohol selectivity for HAS.


**Table 5.** Performance of CO hydrogenation reported in the literature.

<sup>a</sup> Molar ratio. <sup>b</sup> The ethanol's mass fraction in all alcohols. <sup>c</sup> The mass fraction of the higher alcohols in all alcohols.

Figure 7 presents the carbon monoxide hydrogenation performance for 200-h stability tests of LKCG-0.1 catalyst. Seen from Figure 7, the alcohol's selectivity and CO conversion still maintained stability, which are remained at 19.8% and 41.8%, and the higher alcohols in all alcohols stabilized at 72.8%. The outstanding stability can be owned to the uniform dispersion of the active sites, stable catalyst structure, good sintering resistance, and more Co-Ga interfaces.

**Figure 7.** (**a**) Stability performance and (**b**) alcohols distributions (seen from the illustration) of the LKCG-0.1 catalyst after 200 h reaction at T = 290 ◦C, P = 4 MPa, GHSV = 6000 mL gcat−<sup>1</sup> h−1, and H2/CO/N2 = 8/4/1.

## *2.7. Thermo-Gravimetry (TG)*

Figure 8 exhibited the TG curves of the reduced and used LCG and LKCG-x (x = 0.1 and 0.2) catalysts and the corresponding differential thermal gravity (DTG) curves of the used catalysts. In Figure 8, the weight of the three reduced samples increases in the temperature range of 200–320 ◦C, which is attributed to the oxidation of metal cobalt nanoparticles on the surface of the catalysts. Therefore, the TG profiles of the catalysts after reduction was severed as a datum to explore the carbon deposition amount of the catalysts after reaction. In Figure 8b, two exothermic peaks can be seen for all the samples. The peak located at 300–600 ◦C can be attributed to amorphous carbon; while the other peak at 600–800 ◦C to the graphitized carbon [39]. Seen from Figure 8b, the incorporation of K can significantly reduce the total amount and formation rate of amorphous carbon, and for that K can modulate the composition of the catalysts and produce amount of La2O3, which is beneficial to the coke elimination.

**Figure 8.** (**a**) Thermo-gravimetric (TG) curves of the reduced and used catalysts and (**b**) differential thermal gravity (DTG) curves of the used catalysts.

Seen from the Figure 8, the carbon deposition amounts of LKCG-0.2, LKCG-0.1 and LCG after reaction are 3.9%, 5.3% and 10.7%, respectively; in other words, the addition of K significantly relieves the formation of carbon deposition.

For LKCG-x (x = 0.1 and 0.2) catalysts, the containing carbon content of the two catalysts is almost similar. Compared to LCG catalyst, the adding of K leads to a decrease of carbon deposition. According to the above XRPD and XPS results for the reduced LKCG-x catalysts, the doping of K can modulate the composition of La-Ga-O, generating more La2O3, which has a better carbon-depleting effect. Herein, the formula of CO2 + La2O3 → La2O2CO3 *C* → 2CO + La2O3 is used to illustrate the process of removing carbon deposits during the reaction, indicating that more La2O3 favors the anti-carbon effect of catalysts [19,40–42]. In addition, seen from the used XRPD pattern for LKCG-x catalysts, both La2O3 and La2O2CO3 can also be detected, explaining that the above mechanism is correct. Therefore, the K-doped catalyst exhibits the best anti-carbon deposition performance.

For the LCG catalyst, seen from the used XRPD result, no La2O3 and La2O2CO3 can be detected. Meanwhile, there is a strong effects between La and Ga, which is not conducive to eliminating carbon deposited, and thus the carbon content of the LCG catalyst is largest.
