Study on the Modification of Ultra-low Mercury Catalysts for Acetylene Hydrochlorination

Introduction: Industrial hydrochlorination of acetylene currently relies on low-mercury catalysts containing less than 6 % mercury chloride (HgCl2). To further mitigate environmental risks, this study aims to develop an ultralow-mercury catalyst with substantially reduced Hg loading while maintaining high catalytic performance. Methods: Three activated carbon (AC) supports-coconut shell-, wood-, and coalderived- were screened using a low-mercury catalyst formulation. The effects of metal chloride promoters (Co, In, Bi) on catalytic activity and selectivity were systematically evaluated. Additional optimization was performed by incorporating tetramethylammonium chloride (TMAC), 1-ethyl-3-methylimidazolium chloride ([EMIm] Cl), and acetylacetone (acac) as modifiers. Results: Coconut shell AC exhibited the highest catalytic activity and stability, attributable to its low ash content, high surface area, and favorable functional group distribution. Mechanistic analysis revealed that bimetallic Co-In synergy markedly enhanced the catalytic efficiency of Hg, whereas Bi showed negligible influence. Further modification with acetylacetone (2Hg-6Co-4In-5acac/AC) produced activity comparable to commercial benchmarks while substantially lowering Hg content. Discussion: The superior performance of the coconut shell AC-supported catalyst highlights the pivotal role of support properties in determining catalytic behavior. The observed Co-In synergy establishes a new framework for efficient mercury utilization, wherein coordinated bimetallic promotion enables significant Hg reduction without diminishing active site integrity. The strong performance of acetylacetonemodified catalysts further validates this design strategy. Conclusion: This study demonstrates a highly efficient ultralow-mercury catalyst for acetylene hydrochlorination, achieving major reductions in Hg usage without compromising catalytic performance. These findings offer a sustainable route to decreasing mercury dependence in vinyl chloride production, aligning with both environmental and industrial priorities.