Development of Novel Catalysts for Hydrogen Gas production from Biomass Compounds

Authors

Boanerges Bamaca, University of Nebraska-LincolnFollow

First Advisor

Sibel Irmak

Second Advisor

Mark Wilkins

Date of this Version

8-2020

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Agricultural and Biological Systems Engineering

Under the supervision of Professors Sibel Irmak and Mark Wilkins

Lincoln, Nebraska, August 2020

Comments

Copyright 2020, Boanerges Elias Bamaca Saquic. Used by permission

Abstract

Hydrothermal biomass gasification technologies (sub- and supercritical water gasification and aqueous-phase reforming) have considerable economic, environmental, and technical advantages over other energy-extensive technologies (e.g. natural gas reforming) for hydrogen gas production. However, lack of economically feasible and highly active catalysts is a main challenge that impedes upscaling of these technologies for hydrogen gas production.

The goal of this study was to develop innovative, economically feasible and active heterogeneous supported metal catalysts for hydrothermal processes for producing hydrogen gas from biomass-derived compounds. Because of its stable structure and chemical inertness, graphene was used as catalyst support. Graphene supported metal catalysts were prepared using different Pt precursors (H₂PtCl₆·6H₂O, PtBr₂, PtCl₂, and PtI₂) and different metals in monometallic (Pt, Ni, and W) and bimetallic (Pt-Ni and Pt-W) combinations for hydrothermal gasification of biomass compounds. The catalysts were prepared by wet impregnation and ultrasound-assisted wet impregnation for comparison. Sequential reduction methods (first chemical reduction with NaBH₄ then thermal reduction with heating at 300 °C under nitrogen flow) were applied to reduce metal precursors on the support. Catalytic activity of the catalysts were tested by aqueous-phase reforming (APR) as a low temperature hydrothermal gasification technology. Glucose as simple biomass compound was used as feed in APR process.

It was found that the size and distribution of metal particles on the graphene support were highly dependent on the metal type and the metal precursor used in the preparation of the catalysts. The 8 wt.% of metal loading was successfully achieved in all catalysts when ultrasound-assisted wet impregnation deposition method was used. When catalyst was prepared using PtCl₂ precursor, the sizes and distributions of Pt particles on graphene were relatively small and uniform with narrow dispersion compared to the catalysts prepared with PtI₂, PtBr₂ and H₂PtCl₂ precursors. Deposition of W particles on graphene exhibited better results than Ni catalysts in terms of metal particle size and distribution. APR results showed that use of different Pt precursor did not change catalytic activity of Pt/graphene catalysts in terms of total gas mixture and hydrogen produced in APR process if ultrasonication was used in wet impregnation process. Combination of Ni and W metals with Pt showed positive synergy and the catalytic performance of bimetallic catalysts was significantly enhanced.

Advisors: Sibel Irmak and Mark Wilkins