Promoting effect of Pd on H2 production from cellulose pyrolysis over mesocellular-foam-supported Ni catalysts

Noble-metal promoters have been added to catalysts for reactions such as steam-methane reforming, but have rarely been applied to systems that produce H2 from larger, biomass-derived molecules, such as polyols or cellulose. We have previously found that nickel catalysts supported on mesocellular-foam-(MCF)-type silica catalyze H2 formation during cellulose pyrolysis, and sought to increase their activity. Thus, palladium-promoted nickel catalysts supported on MCF were prepared, and their activities were tested in cellulose pyrolysis (RT → 800 °C, 40 °C/min) under dry argon. A thermogravimetric analyzer–mass spectrometer (TG–MS) was used to semi-quantitatively monitor the gases, especially H2, that were released during pyrolysis over catalysts with and without Pd promoters. Although the Pd promoters had little impact on the fraction of H2 in the product gas, adding ≥ 0.4 wt.% Pd enhanced the H2 yield from cellulose pyrolysis by increasing the total gas yield from the reaction. Thus the promoter improved H2 yield by enhancing the tar-cracking activity of the catalyst. A 5%Ni/MCF catalyst that was doped with 0.7 wt.% Pd yielded 85 cm3 H2/g cellulose, which was 15% more H2 than was obtained when the catalyst was 5%Ni/MCF.

► Pd–Ni catalysts on mesocellular foam silica were tested in cellulose pyrolysis. ► As little as 0.4 wt.% Pd boosted H2 yield from Ni-catalyzed pyrolysis. ► Best Pd–Ni catalyst enhanced H2 yield by 15% by increasing tar cracking. ► Improvement was seen in the amount of, not the fraction of H2 in, the product gas. ► Pd promoted the reduction of the Ni catalyst.