Sulphur is much stronger than Carbon as a poison in IC and Xic but same in Pauling Xp （2.5）
American Huilin Institute http://www.amhuilin.com
There are some arguments about the values of electronegativities of carbon, sulphur, selenium, tellurium, iodine and hydrogen . The Chart 1 shows IC values in the order:
Se2+ (3.146)>S2+ (3.121)> C2+ (2.998) >Te2+ (2.832) > I+ (2.530) > H+ (2.297)
The results are consistent with the observations that hydrides H2Se, H2S, H2C, H2Te and HI form H3O+ ions in water  .
As Thomas reviewed, the electronegativity of carbon and sulphur in most of the scale are almost identical. The key point, however, so far as their role as poisons is concerned, is that they differ markedly in the distance at which they sit on the nickel overlayers . The calculations for these locations show that sulphur is very much stronger than carbon as a poison.
The results are also consistent with the experiment data of the dipole moment which indicates that the electron clouds on the C-S and C-I bond in the molecules CS2 and CI4 are close to the sulphur end and the iodine end, respectively . From IC model data (Chart 3.3.3) we can see that S6+ has a greater ionicity than that of C4+: Iav (S6+ = 46.077, C4+=37.015), although they have the close spatial covalency, n*rc-1 (C4+=2.618, S6+=2.805) (Chart 3.3.4).
 Zhang, Y. Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales. Int. J. Mol. Sci. 2010, 11, 4381-4406
 L. Pauling, J. Am. Chem. Soc. 69， 542 (1947).
 Z.-H. Li, Y.-M. Dai, S.-N. Wen, C.-M. Nie, C.-Y. Zhou, Acta Chim. Sin. 63, 14 (2005) 1348
 Dalian University of Technology, Inorg. Chem. (in Chinese), 3rd ed., High Education Press, Beijing, 1990, p.638 and 804.
 J.M. Thomas, Principles and Practice of Heterogeneous Catalysis, Wiley-VCH, 1996, p. 448.
 G.-X. Xu, Material Structure (in Chinise), People’s Education Press, Beijing, 1961, p.160.