Recent studies suggest the use of microwave energy in activated carbon (AC) production emphasizing efficiency specifically in the pyrolysis step as it can significantly reduce heating time compared to conventional furnaces. However, there is no documented effort on the effect of the activating chemical agent on microwave heating dynamics and its impact on pyrolysis time despite its importance for efficiency on both technical and economic aspects of the process. Elucidating the heating rate of H3PO4-activated biomass under microwave energy is one of the objectives of the research while the ultimate goal is to find practical H3PO4 concentration for chemical activation of biomass precursors in obtaining optimum AC yield and textural characteristics. It was found that excessive H3PO4 has a negative effect of slowing down pyrolysis time as it promotes poor microwave absorption on the biomass–H3PO4 complex. In addition, H3PO4 undergoing conversion to its anhydride, P2O5, requires relatively high activation energy, and its conversion may possibly cause extended pyrolysis time. Numerical optimization revealed chemical activation at 56.50% H3PO4, and pyrolysis under 650 W microwave power is a rational balance in terms of maximizing yield and surface area while minimizing activating agents and microwave energy. Under these conditions, a pyrolysis time of around 30 min, yield at around 39.65 wt %, and surface area of 826.38 m2/g can be expected. However, surface area can be as high as 1726.5 m2/g but will require 84.83% H3PO4 on activation, about 803.75 W power and 48 min carbonization time.

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The activated carbons (ACs) enriched in P-containing functional groups were obtained through one-pot microwave-induced pyrolysis from corn stover activated with phosphoric acid and were further tested as the catalyst for selective monophenol production from cellulose pyrolysis for the first time. Maximum AC yield (44.3 wt %) was obtained with an acid to biomass ratio of 0.85. Increasing phosphoric acid to corn stover ratios could enhance the porosity and peak intensities of Pcontaining functional groups in obtained ACs. Attained ACs had an excellent catalytic performance in phenol production with the highest selectivity of phenol (99.02 % based on peak area) in the obtained organic compounds at the catalytic temperature of 450 °C. The catalytic performance of ACs remained highly selective for phenol after using two times. The experimental results indicated that P-containing groups such as −O−P, OP, and −O−P−O− were the active reaction sites and more mespores promoted phenol production. The phenol can be generated from reforming of levoglucosenone and furfural over AC catalysts. The present work provides an efficient route to produce high selective monophenol from cellulose pyrolysis by using activated carbons as the catalyst, which further advanced the utilization of biomass to produce high-value chemicals.