Catalytic conversions of biomass to different energy forms are promising technologies to bridge the gap between the large energy demand and the shortage of fossil fuels. Aqueous phase processing (APP) of biomass derived feedstocks has received much attention after the discovery of aqueous phase reforming (APR) in 2002. As most oxides gradually dissolve in the reaction conditions of APP, carbon is a perfect candidate for the catalyst support of APP, due to its insolubility in aqueous solutions.
Carbon nanotubes (CNTs), including both single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), is a recently discovered novel carbon materials with well-ordered tubular structures. CNTs have been used as catalyst support shortly after its discovery, and have shown advantage over other forms of carbon due to its unique electronic, sorptive and structural properties.
My research has been largely focused on APR over CNT supported catalysts. We have demonstrated that our lab-made SWNTs is an efficient support for APR catalysts. Both monometallic Pt-SWNT and bimetallic Pt-Co-SWNT catalysts show higher catalyst mass time yield (up to ten times) than corresponding Pt and Pt-Co catalysts supported on oxide supports. We have developed two kinds of bimetallic catalysts, one with separate Pt and Co particles as bifunctional catalyst, and the other with Pt-Co alloy phase, while both shows much higher yield than alumina supported Pt-Co catalyst.
One of the advantage of carbon as a catalyst support is that its surface properties are tunable upon chemical functionalization. We studied the effect of CNT surface functional groups on the APR activity, and showed that the hydrophilicity of the carbon support is an important issue controlling the activity of aqueous processing. We have also studied other metal-support interactions in Pt-CNT system, such as the CNT radius of curvature effect, the relative location of the catalytic particles inside or outside CNTs, etc.
It should be noted that our lab-made SWNT shows much better performance as a catalyst support than all the commercially available CNTs. The reason is not clear but could be possibly that our SWNT has a surface area as high as 1800m2/g, the highest surface area ever reported for CNTs. We also studied the production of SWNT aiming to increase its yield and lower the production cost. We have demonstrated an SWNT yield (defined as the weight of SWNT produced per unit weight of catalyst) as high as 75%, which is ten times higher than the commercial CoMoCAT technology. Detailed spectroscopic study also showed that the formation of highly dispersed cobalt silicate species is the key step for successful preparation of catalyst for SWNT production.