Silica-immobilized sulfur compounds as solid calibrants for temperature-programmed reduction and probes for the thermal behavior of organic sulfur forms in fossil fuels / by Ismail, K, Mitchell, S. C., Brown, S. D., Snape, C. E., Buchanan, A. C., Britt, P. F., Franco, D. V., Maes, I. I., Yperman, J.