Oxford Catalysts Research Finds Preparation Method Rather Than Metals Used has Greater Influence on HDS Catalyst Performance
While there is a growing global regulatory trend to ultra low-sulfur diesel and gasoline fuels with their concomitant improvements in emissions, the available crude fuel stocks are increasingly heavier and more sour (higher in sulfur). This combination puts a great deal of importance on high efficiency hydrodesulfurization (HDS) catalysts, especially for the upgrading of heavy oils and residua.
Experiments carried out at Oxford Catalysts suggest that the preparation method has a greater influence on the performance of HDS catalysts than the identity or combination of metals used. Oxford Catalysts offers a novel class of catalysts made from metal carbides which can match or exceed the benefits of traditional precious metal catalysts for applications such as Fischer-Tropsch processing or hydro-desulfurization (HDS) at a lower cost. (Earlier post.)
In a talk presented at the 235th American Chemical Society Meeting last week, Dr. Tiancun Xiao described studies carried out in collaboration with his Oxford Catalyst colleagues, Drs. Sergio Gonzáles-Cortés and Sreekala Rugmini, that demonstrated improved performance in HDS catalysts created using Oxford Catalysts’ patented organic matrix combustion preparation method compared to those containing the same metals but produced using standard impregnation methods.
The organic matrix combustion method, developed by Oxford Catalysts co-founders Professor Malcom Green and Dr. Xiao, prepares, activates and optimizes a supported catalyst in the presence of one or more organic compounds and a transition metal compound which are mixed and combusted under a specific atmosphere. The result is better distribution of the active component on the catalyst support material, thereby improving performance.
HDS catalysts typically consist of one or more metals, such as molybdenum, tungsten, nickel and cobalt, and can be either unpromoted, singly promoted or doubly promoted. Monometallic HDS catalysts are normally made up of molybdenum or tungsten on an alumina support. Bimetallic promoted HDS catalysts typically consist of a molybdenum or tungsten support with nickel or cobalt promoters. Trimetallic promoted catalysts are generally double promoted, with for example, cobalt and nickel promoters.
The group’s experiments revealed that monometallic (Mo, W), bimetallic (NiMo, NiW and CoMo) and trimetallic (NiCoMo and NiCoW) HDS catalysts prepared using organic matrix combustion performed better than HDS catalysts of similar compositions prepared using impregnation methods.
When comparing the performance of different types of HDS catalysts prepared using the organic matrix method, the group found—as expected—that the bimetallic performed better than the monometallic catalysts. However, the performance of the trimetallic catalysts—though still better than that of catalysts prepared via impregnation—was worse than that of the bimetallic catalysts.
The addition of Co (or Ni) on Mo (or W) strongly improved the HDS behavior. However, the addition of Co-Ni on Mo and/or W hindered the HDS performance. This latter effect is attributed to the formation of Ni-Co-S rather than Ni(Co)-Mo(W)-S phase. Urea-matrix combustion method facilitates the formation of well-dispersed oxidic precursors on the alumina surface. This is reflected in a strong synergistic effect that markedly increases the C-S bond cleavage reaction whereas a less pronounced antagonistic effect affects the relative rate of hydrogen transfer reactions.
Insight into the HDS catalytic performance of Co- and/or Ni-promoted Mo and/or W sulfide catalysts (ACS National Meeting, FUEL 194)