A plethora of metal promoters have been applied to enhance the performance of In₂O₃ in CO₂ hydrogenation to methanol, a prospective energy carrier. However, the lack of systematic catalyst preparation and evaluation precludes a direct comparison of their speciation and promotional effects, and consequently, the design of an optimal system. Herein, flame spray pyrolysis (FSP) is employed as a standardized synthesis method to introduce nine metal promoters (0.5 wt.%) into In₂O₃. Methanol productivity generally increased on M-In₂O₃ with selectivity following Pd ≈ Pt > Rh ≈ Ru ≈ Ir > Ni ≈ Co > Ag ≈ In₂O₃ > Au. In-depth characterization, kinetic analyses, and theoretical calculations reveal a range of metal-dependent speciation which dictate catalyst architecture and degree of promotion. Atomically-dispersed promoters (Pd, Pt, Rh, Ru, and Ir) grant the highest improvement in performance, particularly Pd and Pt, which markedly promote hydrogen activation while hindering undesired CO formation. In contrast, metals in clustered (Ni and Co) and nanoparticle (Ag and Au) forms display moderate and no promotion, respectively. This study provides an atomic-level understanding of In₂O₃ promotion based on a unified protocol, and highlights the potential of FSP to engineer complex catalytic systems toward more efficient energy transformations.