The direct synthesis of dimethyl ether (DME) is an ideal process to achieve the environmental objective of CO₂ conversion together with the economic objective of DME production. The effect of the reaction conditions (temperature, pressure, space time) and feed composition (ternary mixtures of H₂ + CO + CO₂ with different CO₂/CO and H₂/CO_x molar ratios) on the reaction indices (CO_x conversion, product yield and selectivity, CO₂ conversion) has been studied by means of experiments carried out in a fixed-bed reactor, with a CuO-ZnO-MnO/SAPO-18 catalyst, in order to establish suitable ranges of operating conditions for enhancing the individual objectives of CO₂ conversion and DME yield. The optimums of these two objectives are achieved in opposite conditions, and for striking a good balance between both objectives, the following conditions are suitable: 275–300 °C; 20–30 bar; 2.5–5 g_cat h (mol_C)⁻¹ and a H₂/CO_x molar ratio in the feed of 3. CO₂/CO molar ratio in the feed is of great importance. Ratios below 1/3 are suitable for enhancing DME production, whereas CO₂/CO ratios above 1 improve the conversion of CO₂. This conversion of CO₂ in the overall process of DME synthesis is favored by the reverse water gas shift equation, since CO is more active than CO₂ in the methanol synthesis reaction.