Aqueous phase reforming of biomass derived oxygenated hydrocarbons for the production to hydrogen

1. Aqueous phase reforming of biomass derived oxygenated hydrocarbons for the production to hydrogen Lisa Mc Aleer Principal Investigators: Farid Aiouache, QuanGan, Mohammad Ahmad

2. Project Summary Investigate use of novel nanoparticle catalysts in aqueous phase reforming (APR) of biomass derived compounds to produce H2. Ni and Pd impregnated on various nanosize supports used to investigate APR of sorbitol to produce H2. Current processes for production of H2, steam reforming and gasification, are demanding in energy, whereas APR can be conducted at low temperatures. Potential for industrial applications using H2 to power fuel cells. Start date: Sept 2007 End date: Sept 2010

3. Objectives • Study mono and bimetallic Ni and Pd catalysts of various metal loadings for low temperature APR of sorbitol. • Achieve high selectivity towards hydrogen and high conversion to CO2. • Analysis of fresh and spent catalysts will help investigate selectivity issues involved. • Exploring the mechanisms involved through extensive kinetic studies and ATR studies.

4. Potential exploitation • Aqueous phase carbohydrates found in waste water from biomass processing and • carbohydrate streams extracted from corn and sugar beets. • Batch reactor can be scaled up to produce high amounts of hydrogen. • Industrial applications of H2 • Hydrogen fuel cells • Chemical feedstock for fertilizers • Chemical reagent – hydrogenation of • carbohydrates to produce glycols • Internal combustion engine, H2 very clean

5. Potential benefits Sorbitol - model carbohydrate compound for biomass undergoing APR to produce H2 Biomass -$5-36 per barrel Crude Oil - $56 per barrel APR can handle biomass resources with high water content, steam reforming needs to volatilize these resources first. APR less demanding in energy than steam reforming H2- clean and mobile energy fuel source used in automobile industry. CO2- recycled back into environment, consumed to grow more biomass Alkane by-products - used to produce biodiesel

6. Schematic representation of reaction pathways for APR of carbohydrates H2 selectivity controlled by altering active metal and metal alloy components and catalyst support

7. Challenges Efficient catalysts for APR must: Facilitate C-C bond cleavage Promote removal of adsorbed CO species by water gas shift (WGS) reaction CO + H2O CO2 + H2 Water Gas Shift Inhibit rate of both C-O bond cleavage and hydrogenation of CO or CO2 which leads to formation of alkanes Selectivity controlled by active metal compounds and supports Pt/Al2O3: active and selective for production of H2 from APR of ethylene glycol. This study investigates cheaper catalysts which will have good activity for APR and find suitable conditions for maximium APR activity and selectivity to H2

8. Catalyst Preparation • Three types of supports were used: • Non reducible support: • -phase aluminium oxide (Alfa Aesar 20nm APS powder), • Reducible support: • cerium (IV) oxide (Alfa Aesar 15-30nm APS powder) and zirconium (IV) oxide (Alfa Aesar 30-50nm APS powder). • Precursors: • Nickel (II) nitrate hexahydrate (Aldrich) • Palladium (II) chloride (Aldrich) • Procedures: • Wet impregnation of appropriate amounts of precursor solution onto supports, followed by stirring for 24 hours. • Dried overnight at 363K followed by calcination at 773K.

9. Catalyst Characterization Ni-Pd/Al2O3 (4.75:0.25wt%) has highest CO uptake, therefore the highest number of active metal sites. Addition of Pd appears to increase the number of active metal sites Table 1: CO uptake of catalysts obtained from CO chemisorption.

10. ‘free’ nickel oxide on support formation of Ni-Pd alloy ‘fixed’ nickel oxide on support formation of spinels of Ni-Al oxides decomposition of nickel nitrate Figure 1. Temperature programmed reduction profiles of Ni and Ni-Pd supported on nanosize Al2O3 support ◊Ni/Al2O3 (5wt%) ▲Ni/Al2O3 (28wt%)+ Ni-Pd/Al2O3 (4.75:0.25wt%) ■Ni-Pd/Al2O3 (4.85:0.15wt%)

11. 2. Catalytic Testing Feedstock Sorbitol– oxygenated hydrocarbon, model for APR of biomass. C6H14O6 + 6H2O 6CO2 + 13H2 Figure 2. Parr 4842 reactor, schematic representation of reactor with online Clarus 400 GC with TCD. H1: heating jacket, T1: thermocouple connected from Parr reactor to temperature control box, S1: stirrer, B1: back pressure regulator, C1: cylinder filled with silica gel.

12. Reaction Conditions • Temperatures: 498-523K • Pressures: 60 bar Ar carrier gas • Feed concentrations: 5wt% in DI water • Stirring speed: 800rpm Definitions CO2 selectivity: mole number of CO2 in gas phase normalized by total mole number of carbon in gas phase % Conversion to CO2: conversion of sorbitol to total carbon products x CO2 selectivity/ 100 % H2 selectivity: (mole number of H2 produced/ total mole number of carbon in gas phase) x (1/RR*) x 100 *RR is H2/CO2 reforming ratio which is 13/6 for sorbitol

13. Figure 3. Conversion of sorbitol to CO2 and selectivity to H2 over Ni/Al2O3catalysts at different temperatures. □Ni/Al2O3 (5wt%) at 498K, ■Ni/Al2O3 (5wt%) at 523K, Ni/Al2O3 (28wt%) at 498K, ▲ Ni/Al2O3 (28wt%) at 523K, x Ni/Al2O3 (40wt%) at 523K • Ni/Al2O3(5wt%) : • Low conversion at both temperatures • Higher initial selectivity to H2 due to sorbitol degradation (minimum reforming). • Ni/Al2O3 (28wt%): • High conversions and high catalyst loading

14. Figure 4: Conversion of sorbitol to CO2 and selectivity to H2 over Ni and Ni-Pd/Al2O3 catalysts at 498K. xNi/Al2O3 (5wt%) ▲ Ni/Al2O3 (28wt%) ■ Ni-Pd/Al2O3 (4.75:0.25wt%) ● Ni-Pd/Al2O3 (4.85:0.15wt%) • Ni-Pd/Al2O3 (4.75:0.25wt%) : High selectivity to H2 but • Sorbitol degradation was relevant during the first 3 hours • Sorbitol reforming was relevant beyond 4 hours (high conversions to CO2) • Ni-Pd/Al2O3(4.85:0.15wt%) • Better conversion than monometallic Nickel catalyst with same metal loading. • Selectivity steadily increasing • Adding just a small amount of Pd increased conversion and prevented initial sorbitol degradation

15. Figure 5. Conversion to CO2 and selectivity to H2 over Ni-Pd (4.75:0.25wt%) on different supports at 498K ( ) Conversion to CO2: ● Ni-Pd/Al2O3■ Ni-Pd/ZrO2x Ni-Pd/CeO2 ( ) Selectivity to H2: ● Ni-Pd/Al2O3■ Ni-Pd/ZrO2 x Ni-Pd/CeO2 • Both Ni-Pd/ZrO2and Ni-Pd/CeO2 show very poor conversion but high selectivity due to sorbitol degradation. • Poor APR activity for ZrO2 and CeO2 is due to lower Bronsted acidity of these supports compared to Al2O3. • Results different from steam reforming where reducible supports exhibit synergetic activity

16. TurnoverFrequencies TOF values eliminate the effect of metal loading on the support. Ni/Al2O3 (28) – Highest TOF value so production of CO2 is fastest during the first hour Table 2: TOF calculated as mols of CO2/ mols of Ni based on CO uptake normalized by time

17. TGA results of Ni/Al2O3 (28wt%) TGA results of Ni-Pd/Al2O3 (4.75:0.25wt%) TGA results of Ni/Al2O3 (5wt%) TGA results of Ni-Pd/Al2O3 (4.85:0.15 wt%)

18. Future Work • Extensive kinetic studies using rate orders to propose the mechanism of APR of sorbitol • ATR studies of WGS reaction over Pd/Al2O3

19. Summary of Results • Addition of Pd to Ni/Al2O3 catalysts has many effects: • Improves reducibility of Ni/Al2O3 catalysts • Increases number of active metal sites on catalyst • Increases conversion of sorbitol to CO2 • Decreases initial sorbitol degradation so H2 selectivity is due to reforming only XRD studies will confirm whether free or fixed nickel oxide on Al2O3 support TPD followed by TPO will confirm what forms of carbon are deposited on catalyst and will help confirm reaction pathways Extensive kinetic studies will help propose the mechanism for APR of sorbitol and the parallel selectivity pathways

20. Changes to project Catalyst preparation and GC problems did not allow progress towards engineering step in project Implications of project APR of various biomass wastes in Northern Ireland to produce H2 is feasible. Testing of more bi or multicatalysts by high throughput reactors Moving towards the proposed reactor system for combined reaction and simultaneous gas separation