**1. Introduction**

Carbon dioxide (CO2) and hydrogen sulfide (H2S) are often considered as harmful waste gases, coexisting in many industries. These massive acid gases must be harmlessly treated for environmental improvement. Particularly, converting CO2 and H2S acid gases into value-added products will bring about more environmental and economic benefits. However, CO2 is an extremely stable molecule that commonly needs to be activated at high temperature. Hence, converting CO2 into valuable products, such as chemicals and fuels, is a global challenge [1]. Several methods for CO2 conversion have been reported. Traynor et al. [2] revealed that using solar energy could directly reduce CO2. They found that the high-temperature solar irradiance system provided strong heating of CO2 with the resultant dissociation. Huh [3] reported the catalytic cycloaddition reaction of CO2 into organic epoxides to produce cyclic carbonates using MOFs material as e fficient catalysts for this reaction. Furthermore, in recent years, photocatalytic reduction of CO2 has been also an attractive approach [4–6]. A series of new transition-metal-centered electrocatalysts has been developed for the electrocatalytic reduction of CO2 to produce value-added C1 or C2 chemicals [7]. Among the aforementioned methods, the catalytic CO2 conversion seems to be a promising process for its utilization due to the ambient operating conditions.

Hydrogen sulfide is a highly toxic pollutant, and a major source of acid rain when oxidized in the atmosphere. In industry, H2S is usually removed by the Claus process, in which it is partially oxidized to produce water and elemental sulfur [8]. Additionally, Li et al. [9] studied the oxidation process of H2S on activated carbon (AC) to simultaneously capture H2S and SO2. The results indicate that H2S was adsorbed on the AC surface and combined with oxygen-containing functional groups to form sulfate (SO4<sup>2</sup>−) in the absence of O2. Palma et al. [10] investigated the H2S thermal oxidative decomposition at different operating conditions. The results show that the reaction temperature of 1100 ◦C and a O2/H2S ratio equal to 0.2 allowed to achieve the highest H2S conversion and the lowest selectivity to SO2. They also prepared cordierite-honeycomb-structured catalysts for H2S oxidative decomposition at high temperature. It revealed that the optimal washcoat percentage of 30 wt% for the catalysts could obtain high H2S conversion and H2 yield [11]. Previously, we demonstrated that the semiconductor catalysts synergistically working with non-thermal plasma could exhibit excellent performance in H2S decomposition [12–14]. The photons and electric fields generated by the plasma could excite the semiconductor catalyst to generate electron–hole pairs, which dramatically enhanced H2S decomposition.

The above-mentioned studies have been reported for the separate conversion of H2S or CO2. The one-step conversion of CO2 and H2S acid gas to syngas (a mixture of CO and H2) is expected to provide an alternative route to reduce CO2 emissions and detoxify H2S with added environmental and economic benefits. In the present work, we demonstrated a low-temperature and novel non-thermal plasma method aided by Ni-Mo sulfide/Al2O3 catalysts for syngas production from the simultaneous conversion of CO2 and H2S. A series of Ni-Mo sulfide/Al2O3 catalysts with different Ni/Mo molar ratios was prepared. The effects of the chemical and physical properties on the catalytic behaviors of the as-prepared catalysts were carefully investigated by various characterization methods such as XRD, nitrogen sorption, UV-vis, TEM, SEM, ICP, and XPS. Some intensive understandings for the optimizations and designs of catalysts were also provided through studying the structure–performance correlations.

#### **2. Results and Discussion**
