Iron poisoning is a well-known problem for fluid catalytic cracking catalysts. Previously, we have used several characterization techniques, including SEM, TEM and EDX, to examine an iron-poisoned catalyst sample from a commercial unit. The results clearly showed that Fe, as well as some other contaminant metals (such as Ni, Mg and Ca), and Si were enriched on the catalyst particle surface (J. Catal. 2018, 361, 126-134). In this contribution, surface Si enrichment was further studied with many iron poisoned Ecat samples from different refineries. The data was obtained with SEM-EDX measurements of Ecat particles under different accelerating voltages, coupled with Monte Carlo simulations. Surface Si enrichment was found to correlate well with Fe content in the Ecat samples, confirming that both Fe contaminants and Si accumulation on the catalyst surface need to be considered to better understand iron poisoning mechanism and to design more stable catalysts. (C) 2019 Elsevier Inc. All rights reserved.